I know nailed the issue to AeroGearGCMMessageReceiver

This class tries to register a defaultHandler and fails at this statement:

defaultHandler = defaultHandlerClass.newInstance();

with the following error:
java.lang.IllegalAccessException: access to constructor not allowed
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1319)
at org.jboss.aerogear.android.unifiedpush.AeroGearGCMMessageReceiver.onReceive(AeroGearGCMMessageReceiver.java:63)