App crashes on tapping on Admob ads and IAB

We are trying to impliment admob ads though mopub mediation. when we click on the admob banner ad app crash. Same thing happens when I click on purchases button(we are prime31 IAB plugin). It happens only in android 4.4 and above. Following is the crash log:-

 10-22 20:02:14.836: E/AndroidRuntime(6795): FATAL EXCEPTION: main
 10-22 20:02:14.836: E/AndroidRuntime(6795): Process: com.comp.apps, PID: 6795
 10-22 20:02:14.836: E/AndroidRuntime(6795): java.lang.Error: FATAL EXCEPTION [main]
 10-22 20:02:14.836: E/AndroidRuntime(6795): Unity version     : 4.5.4f1
 10-22 20:02:14.836: E/AndroidRuntime(6795): Device model      : LGE Nexus 4
 10-22 20:02:14.836: E/AndroidRuntime(6795): Device fingerprint: google/occam/mako:4.4.4/KTU84P/1227136:user/release-keys
 10-22 20:02:14.836: E/AndroidRuntime(6795): Caused by: java.lang.NullPointerException
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.app.ActionBarImpl.doHide(ActionBarImpl.java:746)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.app.ActionBarImpl.updateVisibility(ActionBarImpl.java:674)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.app.ActionBarImpl.hideForSystem(ActionBarImpl.java:646)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.widget.ActionBarOverlayLayout.onWindowSystemUiVisibilityChanged(ActionBarOverlayLayout.java:151)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.widget.ActionBarOverlayLayout.setActionBar(ActionBarOverlayLayout.java:98)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.app.ActionBarImpl.init(ActionBarImpl.java:182)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.app.ActionBarImpl.<init>(ActionBarImpl.java:166)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.app.Activity.initActionBar(Activity.java:1912)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.app.Activity.getMenuInflater(Activity.java:3347)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.app.Activity.onCreatePanelMenu(Activity.java:2539)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.policy.impl.PhoneWindow.preparePanel(PhoneWindow.java:436)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.policy.impl.PhoneWindow.doInvalidatePanelMenu(PhoneWindow.java:800)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.policy.impl.PhoneWindow$1.run(PhoneWindow.java:221)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.view.Choreographer.doCallbacks(Choreographer.java:574)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.view.Choreographer.doFrame(Choreographer.java:543)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.os.Handler.handleCallback(Handler.java:733)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.os.Handler.dispatchMessage(Handler.java:95)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.os.Looper.loop(Looper.java:136)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at android.app.ActivityThread.main(ActivityThread.java:5001)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at java.lang.reflect.Method.invokeNative(Native Method)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at java.lang.reflect.Method.invoke(Method.java:515)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
 10-22 20:02:14.836: E/AndroidRuntime(6795):     at dalvik.system.NativeStart.main(Native Method)

We are using Unity 4.5.4, Mopub 3.2.0 and latest google play services