OK, I\'ve been extending my activities to
extends ActionBarActivity
My main menu page
extends FragmentActivity
Experienced same problem and the solution, as mentioned in other responses, is to edit your ActionBarActivity class. 
This class is defined in your code (com.google.android.actionbarcompat). The only thing you have to do is change extends Activity to extends FragmentActivity from the android.support.v4.app.FragmentActivity.
ActionBarActivity extends android.support.v4.app.FragmentActivity, so ActionBarActivity serves both purposes.
Do you have menu items for your Fragments? Use your own app namespace instead of android for app:showAsAction and app:actionLayout, etc.
To add your namespace to the XML use this line in the menu tag
xmlns:app="http://schemas.android.com/apk/res-auto"
E.g.
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item android:id="@+id/menu_settings" app:showAsAction="ifRoom" android:title="@string/menu_settings" android:orderInCategory="100" />
</menu>
Note the app:showAsAction rather than android:showAsAction
Is your code from the Action Bar compatibility example that comes with the SDK? If so just change the ActionBarActivity class in that example to extend FragmentActivity (from the compatibility library I assume) instead of Activity.