I'm stuck for a while on a mysterious problem. So I implemented GCM in my android app, but i receive an INVALID_SENDER error.
- My SENDER_ID is the id from the url of the google project.
 - The Android push notifications are ON
 
The weird thing about this is that i already have a registration id to send notifications to. So my console looks like this:
03-26 09:39:20.233: I/<test>(19761): Already registered: APA91bG6-   O3OnZt50EAjYvJ5KETv3qAlPOn2SfOPXez7SLAmaAOkHTN6EMDJb91gFIWkftZkJiub6UoEk4O-  WQP7kk2oZGQjZ1VCZZS0WddQtjFaCfYfZfb7SEw3IS1sd4caJcdZE4LA1F0hxzc7Ss1UiYHXX-XXXX
03-26 09:48:23.522: I/<test>(19925): GCMIntentService 
03-26 09:39:20.670: I/<test>(19761): on Error INVALID_SENDER
Inside the onCreate:
GCMRegistrar.checkDevice(this);
GCMRegistrar.checkManifest(this);
final String regId = GCMRegistrar.getRegistrationId(this);
if (regId.equals("")) {
    Log.i("<test>", "registering");
        GCMRegistrar.register(this, "2194354949XX");
} else {
    Log.i("<test>", "Already registered: " + regId);
}
broadcastreceiver:
 public class GCMBroadcastReceiver extends com.google.android.gcm.GCMBroadcastReceiver{
    @Override
    protected String getGCMIntentServiceClassName(Context context){
        return "be.XXX.XXX.system.GCMIntentService";
    }
}
GCMIntentService:
 public class GCMIntentService extends GCMBaseIntentService {
    @Override
    protected void onError(Context arg0, String errorId) {
        Log.i("<test>","on Error " + errorId);
    }
    @Override
    protected void onMessage(Context arg0, Intent intent) {
        Log.i("<test>","onMessage " + intent.getExtras().toString());
    }
    @Override
    protected void onRegistered(Context arg0, String regId) {
        Log.i("<test>","Registration id: " + regId);
    }
    @Override
    protected void onUnregistered(Context arg0, String regId) {
        Log.i("<test>","onUnregistered " + regId);
    }
    public GCMIntentService() {
        super("2194354949XX");
        Log.i("<test>","GCMIntentService ");
    }
}
Manifest:
 <permission
    android:name="com.XX.XX.permission.C2D_MESSAGE"
    android:protectionLevel="signature" />
<uses-permission android:name="com.smstiming.hezemans.permission.C2D_MESSAGE" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
<uses-permission android:name="android.permission.INTERNET" /> 
<uses-permission android:name="android.permission.GET_ACCOUNTS" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.VIBRATE" />
<receiver android:name="be.XX.XX.system.GCMBroadcastReceiver" android:permission="com.google.android.c2dm.permission.SEND" >
        <intent-filter>
            <action android:name="com.google.android.c2dm.intent.RECEIVE" />
            <action android:name="com.google.android.c2dm.intent.REGISTRATION" />
            <category android:name="com.smstiming.hezemans" />
        </intent-filter>
    </receiver>
 <service android:name="be.XX.XX.system.GCMIntentService" />