It was a working app, both on emulator and the device i am testing on.
But now, i enabled Proguard and Exported the signed app using Android-Tools
The stack trace shows that ActionBarSherlock is failing to find a constructor "a(Activity,int)" using reflection. Its documentation indeed specifies that each extension of ActionBarSherlock should have such a constructor. ProGuard doesn't (can't) know this and has removed the constructor, because it appears unused in the code. You therefore have to explicitly tell ProGuard to keep it:
-keepclassmembers class * extends com.actionbarsherlock.ActionBarSherlock {
(android.app.Activity, int);
}
In general, if you get such stack traces related to reflection in your code or its libraries, you need to add corresponding configuration.