Android Question problem with GCM push services

I have downloaded your example “Push notifications (GCM) framework” ,the app work fine,but I have a problem:

when I send continued messages ( in less than 5-6 secs) from twenty-first message ( 21°) the app no longer receives messages.

So,when I set the phone in modality OFF-LINE and go back the phone in ON-LINE the phone resume the message from queue.

Can you help me?

Thanks,

Lorenzo