Google Maps problems

O.K. I'm trying to learn how to develop Android apps and have been going through a tutorial about using Google Maps within an app using MapView. I've done all the proper stuff in getting an MD5 and API key o enable this to happen and have spent ages trying to get it to work on my Samsung Gaaxy S2 phone - all I get is an image of a grey grid screen with a blue dot flashing in the middle but no map.

In desperation I thought I'd test drive my app on my Asus Nexus 7 tablet and hey presto it works just fine so my question is why isn't teh app woking on the Galaxy S2 when it works fine on the Nexus? USB debugging is turned on by the way.

Thanks for your interest.

OK an update...

I turned the phone off then on and tried the app again and it worked.

Guess I should have thought of that in the first place, durrrrr..