Google Play Game Services causing: Unable to convert classes into dex format

I added the GitHub Google Play Services package to my game. (https://github.com/playgameservices/play-games-plugin-for-unity). When I call the first thing you need to do: "PlayGamesPlatform.Activate();", this happens:

Full error:

CommandInvokationFailure: Unable to convert classes into dex format. See the Console for details. D:/Programmer/Java\bin\java.exe -Xmx2048M -Dcom.android.sdkmanager.toolsdir="D:/Programmer/Android SDK\tools" -Dfile.encoding=UTF8 -jar "D:\Programmer\Unity\Editor\Data\PlaybackEngines\AndroidPlayer/Tools\sdktools.jar" -

stderr[ Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zznm; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zznn; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zzno; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zzno$zza; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zznp; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zznq; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zzqi; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zzqi$zza; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/google/android/gms/internal/zzqj; 9 errors; aborting ] stdout[ processing archive D:\Programmer\Unity\Projects\Pogo Stick Man 2\Temp\StagingArea\android-libraries\MainLibProj\libs.\play-games-plugin-support.jar... ignored resource META-INF/ ignored resource META-INF/MANIFEST.MF ignored resource com/ ignored resource com/google/ ignored resource com/google/games/ ignored resource com/google/games/bridge/ processing com/google/games/bridge/BuildConfig.class... processing com/google/games/bridge/NativeBridgeActivity.class... processing com/google/games/bridge/TokenFragment.class... processing com/google/games/bridge/TokenFragment$1.class... processing com/google/games/bridge/TokenFragment$TokenRequest.class... processing com/google/games/bridge/TokenPendingResult.class... processing com/google/games/bridge/TokenResult.class... processing archive D:\Programmer\Unity\Projects\Pogo Stick Man 2\Temp\StagingArea\android-libraries\appcompat-v7-23.1.1\libs.\classes.jar... ignored resource .readme ignored resource META-INF/ ignored resource META-INF/MANIFEST.MF ignored resource android/ ignored resource android/support/ ignored resource android/support/v7/ ignored resource android/support/v7/app/ processing android/support/v7/app/ActionBar.class... processing android/support/v7/app/ActionBar$DisplayOptions.class... processing android/support/v7/app/ActionBar$LayoutParams.class... processing android/support/v7/app/ActionBar$NavigationMode.class... processing android/support/v7/app/ActionBar$OnMenuVisibilityListener.class... processing android/support/v7/app/ActionBar$OnNavigationListener.class... processing android/support/v7/app/ActionBar$Tab.class... processing android/support/v7/app/ActionBar$TabListener.class... processing android/support/v7/app/ActionBarActivity.class... processing android/support/v7/app/ActionBarDrawerToggle.class... processing android/support/v7/app/ActionBarDrawerToggle$1.class... processing android/support/v7/app/ActionBarDrawerToggle$Delegate.class... processing android/support/v7/app/ActionBarDrawerToggle$DelegateProvider.class... processing android/support/v7/app/ActionBarDrawerToggle$DrawerArrowDrawableToggle.class... processing android/support/v7/app/ActionBarDrawerToggle$DrawerToggle.class... processing android/support/v7/app/ActionBarDrawerToggle$DummyDelegate.class... processing android/support/v7/app/ActionBarDrawerToggle$HoneycombDelegate.class... processing android/support/v7/app/ActionBarDrawerToggle$JellybeanMr2Delegate.class... processing android/support/v7/app/ActionBarDrawerToggle$ToolbarCompatDelegate.class... processing android/support/v7/app/ActionBarDrawerToggleHoneycomb.class... processing android/support/v7/app/ActionBarDrawerToggleHoneycomb$SetIndicatorInfo.class... processing android/support/v7/app/AlertController.class... processing android/support/v7/app/AlertController$1.class... processing android/support/v7/app/AlertController$2.class... processing android/support/v7/app/AlertController$3.class... processing android/support/v7/app/AlertController$4.class... processing android/support/v7/app/AlertController$5.class... processing android/support/v7/app/AlertController$AlertParams.class... processing android/support/v7/app/AlertController$AlertParams$1.class... processing android/support/v7/app/AlertController$AlertParams$2.class... processing android/support/v7/app/AlertController$AlertParams$3.class... processing android/support/v7/app/AlertController$AlertParams$4.class... processing android/support/v7/app/AlertController$AlertParams$OnPrepareListViewListener.class... processing android/support/v7/app/AlertController$ButtonHandler.class... processing android/support/v7/app/AlertController$CheckedItemAdapter.class... processing android/support/v7/app/AlertDialog.class... processing android/support/v7/app/AlertDialog$Builder.class... processing android/support/v7/app/AppCompatActivity.class... processing android/support/v7/app/AppCompatCallback.class... processing android/support/v7/app/AppCompatDelegate.class... processing android/support/v7/app/AppCompatDelegateImplBase.class... processing android/support/v7/app/AppCompatDelegateImplBase$1.class... processing android/support/v7/app/AppCompatDelegateImplBase$ActionBarDrawableToggleImpl.class... processing android/support/v7/app/AppCompatDelegateImplBase$AppCompatWindowCallbackBase.class... processing android/support/v7/app/AppCompatDelegateImplV11.class... processing android/support/v7/app/AppCompatDelegateImplV14.class... processing android/support/v7/app/AppCompatDelegateImplV14$AppCompatWindowCallbackV14.class... processing android/support/v7/app/AppCompatDelegateImplV23.class... processing android/support/v7/app/AppCompatDelegateImplV23$AppCompatWindowCallbackV23.class... processing android/support/v7/app/AppCompatDelegateImplV7.class... processing android/support/v7/app/AppCompatDelegateImplV7$1.class... processing android/support/v7/app/AppCompatDelegateImplV7$2.class... processing android/support/v7/app/AppCompatDelegateImplV7$3.class... processing android/support/v7/app/AppCompatDelegateImplV7$4.class... processing android/support/v7/app/AppCompatDelegateImplV7$5.class... processing android/support/v7/app/AppCompatDelegateImplV7$5$1.class... processing android/support/v7/app/AppCompatDelegateImplV7$6.class... processing android/support/v7/app/AppCompatDelegateImplV7$ActionMenuPresenterCallback.class... processing android/support/v7/app/AppCompatDelegateImplV7$ActionModeCallbackWrapperV7.class... processing android/support/v7/app/AppCompatDelegateImplV7$ActionModeCallbackWrapperV7$1.class... processing android/support/v7/app/AppCompatDelegateImplV7$ListMenuDecorView.class... processing android/support/v7/app/AppCompatDelegateImplV7$PanelFeatureState.class... processing android/support/v7/app/AppCompatDelegateImplV7$PanelFeatureState$SavedState.class... processing android/support/v7/app/AppCompatDelegateImplV7$PanelFeatureState$SavedState$1.class... processing android/support/v7/app/AppCompatDelegateImplV7$PanelMenuPresenterCallback.class... processing android/support/v7/app/AppCompatDialog.class... processing android/support/v7/app/AppCompatDialogFragment.class... processing android/support/v7/app/AppCompatViewInflater.class... processing android/support/v7/app/AppCompatViewInflater$DeclaredOnClickListener.class... processing android/support/v7/app/NavItemSelectedListener.class... processing android/support/v7/app/NotificationCompat.class... processing android/support/v7/app/NotificationCompat$1.class... processing android/support/v7/app/NotificationCompat$Builder.class... processing android/support/v7/app/NotificationCompat$IceCreamSandwichExtender.class... processing android/support/v7/app/NotificationCompat$JellybeanExtender.class... processing android/support/v7/app/NotificationCompat$LollipopExtender.class... processing android/support/v7/app/NotificationCompat$MediaStyle.class... processing android/support/v7/app/NotificationCompatImpl21.class... processing android/support/v7/app/NotificationCompatImplBase.class... processing android/support/v7/app/ToolbarActionBar.class... processing android/support/v7/app/ToolbarActionBar$1.class... processing android/support/v7/app/ToolbarActionBar$2.class... processing android/support/v7/app/ToolbarActionBar$ActionMenuPresenterCallback.class... processing android/support/v7/app/ToolbarActionBar$MenuBuilderCallback.class... processing android/support/v7/app/ToolbarActionBar$PanelMenuPresenterCallback.class... processing android/support/v7/app/ToolbarActionBar$ToolbarCallbackWrapper.class... processing android/support/v7/app/TwilightCalculator.class... processing android/support/v7/app/TwilightManager.class... processing android/support/v7/app/TwilightManager$1.class... processing android/support/v7/app/TwilightManager$TwilightState.class... processing android/support/v7/app/WindowDecorActionBar.class... processing android/support/v7/app/WindowDecorActionBar$1.class... processing android/support/v7/app/WindowDecorActionBar$2.class... processing android/support/v7/app/WindowDecorActionBar$3.class... processing android/support/v7/app/WindowDecorActionBar$ActionModeImpl.class... processing android/support/v7/app/WindowDecorActionBar$TabImpl.class... ignored resource android/support/v7/appcompat/ processing android/support/v7/appcompat/BuildConfig.class... ignored resource android/support/v7/graphics/ ignored resource android/support/v7/graphics/drawable/ processing android/support/v7/graphics/drawable/DrawableUtils.class... processing android/support/v7/graphics/drawable/DrawableWrapper.class... processing android/support/v7/graphics/drawable/DrawerArrowDrawable.class... processing android/support/v7/graphics/drawable/DrawerArrowDrawable$ArrowDirection.class... ignored resource android/support/v7/text/ processing android/support/v7/text/AllCapsTransformationMethod.class... ignored resource android/support/v7/transition/ processing android/support/v7/transition/ActionBarTransition.class... ignored resource android/support/v7/view/ processing android/support/v7/view/ActionBarPolicy.class... processing android/support/v7/view/ActionMode.class... processing android/support/v7/view/ActionMode$Callback.class... processing android/support/v7/view/CollapsibleActionView.class... processing android/support/v7/view/ContextThemeWrapper.class... processing android/support/v7/view/StandaloneActionMode.class... processing android/support/v7/view/SupportActionModeWrapper.class... processing android/support/v7/view/SupportActionModeWrapper$CallbackWrapper.class... processing android/support/v7/view/SupportMenuInflater.class... processing android/support/v7/view/SupportMenuInflater$InflatedOnMenuItemClickListener.class... processing android/support/v7/view/SupportMenuInflater$MenuState.class... processing android/support/v7/view/ViewPropertyAnimatorCompatSet.class... processing android/support/v7/view/ViewPropertyAnimatorCompatSet$1.class... processing android/support/v7/view/WindowCallbackWrapper.class... ignored resource android/support/v7/view/menu/ processing android/support/v7/view/menu/ActionMenuItem.class... processing android/support/v7/view/menu/ActionMenuItemView.class... processing android/support/v7/view/menu/ActionMenuItemView$ActionMenuItemForwardingListener.class... processing android/support/v7/view/menu/ActionMenuItemView$PopupCallback.class... processing android/support/v7/view/menu/BaseMenuPresenter.class... processing android/support/v7/view/menu/BaseMenuWrapper.class... processing android/support/v7/view/menu/BaseWrapper.class... processing android/support/v7/view/menu/ExpandedMenuView.class... processing android/support/v7/view/menu/ListMenuItemView.class... processing android/support/v7/view/menu/ListMenuPresenter.class... processing android/support/v7/view/menu/ListMenuPresenter$MenuAdapter.class... processing android/support/v7/view/menu/MenuBuilder.class... processing android/support/v7/view/menu/MenuBuilder$Callback.class... processing android/support/v7/view/menu/MenuBuilder$ItemInvoker.class... processing android/support/v7/view/menu/MenuDialogHelper.class... processing android/support/v7/view/menu/MenuItemImpl.class... processing android/support/v7/view/menu/MenuItemImpl$1.class... processing android/support/v7/view/menu/MenuItemWrapperICS.class... processing android/support/v7/view/menu/MenuItemWrapperICS$ActionProviderWrapper.class... processing android/support/v7/view/menu/MenuItemWrapperICS$CollapsibleActionViewWrapper.class... processing android/support/v7/view/menu/MenuItemWrapperICS$OnActionExpandListenerWrapper.class... processing android/support/v7/view/menu/MenuItemWrapperICS$OnMenuItemClickListenerWrapper.class... processing android/support/v7/view/menu/MenuItemWrapperJB.class... processing android/support/v7/view/menu/MenuItemWrapperJB$ActionProviderWrapperJB.class... processing android/support/v7/view/menu/MenuPopupHelper.class... processing android/support/v7/view/menu/MenuPopupHelper$MenuAdapter.class... processing android/support/v7/view/menu/MenuPresenter.class... processing android/support/v7/view/menu/MenuPresenter$Callback.class... processing android/support/v7/view/menu/MenuView.class... processing android/support/v7/view/menu/MenuView$ItemView.class... processing android/support/v7/view/menu/MenuWrapperFactory.class... processing android/support/v7/view/menu/MenuWrapperICS.class... processing android/support/v7/view/menu/SubMenuBuilder.class... processing android/support/v7/view/menu/SubMenuWrapperICS.class... ignored resource android/support/v7/widget/ processing android/support/v7/widget/AbsActionBarView.class... processing android/support/v7/widget/AbsActionBarView$1.class... processing android/support/v7/widget/AbsActionBarView$VisibilityAnimListener.class... processing android/support/v7/widget/ActionBarBackgroundDrawable.class... processing android/support/v7/widget/ActionBarBackgroundDrawableV21.class... processing android/support/v7/widget/ActionBarContainer.class... processing android/support/v7/widget/ActionBarContextView.class... processing android/support/v7/widget/ActionBarContextView$1.class... processing android/support/v7/widget/ActionBarOverlayLayout.class... processing android/support/v7/widget/ActionBarOverlayLayout$1.class... processing android/support/v7/widget/ActionBarOverlayLayout$2.class... processing android/support/v7/widget/ActionBarOverlayLayout$3.class... processing android/support/v7/widget/ActionBarOverlayLayout$ActionBarVisibilityCallback.class... processing android/support/v7/widget/ActionBarOverlayLayout$LayoutParams.class... processing android/support/v7/widget/ActionMenuPresenter.class... processing android/support/v7/widget/ActionMenuPresenter$1.class... processing android/support/v7/widget/ActionMenuPresenter$ActionButtonSubmenu.class... processing android/support/v7/widget/ActionMenuPresenter$ActionMenuPopupCallback.class... processing android/support/v7/widget/ActionMenuPresenter$OpenOverflowRunnable.class... processing android/support/v7/widget/ActionMenuPresenter$OverflowMenuButton.class... processing android/support/v7/widget/ActionMenuPresenter$OverflowMenuButton$1.class... processing android/support/v7/widget/ActionMenuPresenter$OverflowPopup.class... processing android/support/v7/widget/ActionMenuPresenter$PopupPresenterCallback.class... processing android/support/v7/widget/ActionMenuPresenter$SavedState.class... processing android/support/v7/widget/ActionMenuPresenter$SavedState$1.class... processing android/support/v7/widget/ActionMenuView.class... processing android/support/v7/widget/ActionMenuView$1.class... processing android/support/v7/widget/ActionMenuView$ActionMenuChildView.class... processing android/support/v7/widget/ActionMenuView$ActionMenuPresenterCallback.class... processing android/support/v7/widget/ActionMenuView$LayoutParams.class... processing android/support/v7/widget/ActionMenuView$MenuBuilderCallback.class...

Please help me figure out why this happens! Appreciate answers.