Error in building and signing APK.

Just today, I have a serious problem where I cannot build any APK for Android. Whenever I tried to build an unsigned (debug) APK, there always an error message saying:

 Error building Player: ArgumentException: An empty file name is not valid.

And whenever I tried to sign the app with a keystore that I generated before, after I filled the password and clicked the "Alias" drop down menu, there always this error message:

 ArgumentException: An empty file name is not valid.
 System.IO.FileSystemInfo.CheckPath (System.String path)
 System.IO.DirectoryInfo..ctor (System.String path, Boolean simpleOriginalPath)
 System.IO.DirectoryInfo..ctor (System.String path)
 (wrapper remoting-invoke-with-check) System.IO.DirectoryInfo:.ctor (string)
 UnityEditor.AndroidKeystoreWindow.findPathWildcard (System.String str)
 UnityEditor.AndroidKeystoreWindow.LocateJDKbin ()
 UnityEditor.AndroidKeystoreWindow.setupKeytool ()
 UnityEditor.AndroidKeystoreWindow.GetAvailableKeys (System.String keystore, System.String storepass)
 UnityEditor.PlayerSettingsEditor.PublishSectionGUI (Int32 selectedPlatform)
 UnityEditor.PlayerSettingsEditor.OnInspectorGUI ()
 UnityEditor.InspectorWindow.DrawEditors (Boolean isRepaintEvent, UnityEditor.Editor[] editors, Boolean eyeDropperDirty)
 UnityEditor.InspectorWindow.OnGUI ()
 System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)

This also the case when I tried to build create a new keystore, after I filled in all the details like name, organization, validity etc, the same error message appear after clicking the "Create Key" button.

I didn't do anything with the project and I knew that the keystore works properly as I just used it yesterday.

I'm using Mac OSX Mountain Lion 10.8.2 and Unity Pro 3.5.6f4. Not sure what happened.. I don't want to end up reformatting my mac.

Thanks in advance.