Turning on Airplay and then it turns off itself

so just a few hours ago, I downloaded 'real racing 2' and want to play it on my apple tv (i'm using it with an iphone 4s/ios5). i have used airplay mirroring with it a few times and and never had any issues (for the most part, non-gaming apps).

at first it seemed to work with the game but then suddenly it didn't. i went to check if airplay is switch on but it's not anymore. so i try to switch it back on but it doesn't allow me and switches back to the iphone by itself. even if i set airplay mirroring on it does the same.

after waiting for a little bit and did two restarts with the phone (regular and hard restart), i tried and it works. the game worked ok at first then suddenly it lagged so much that airplay switch off and the game went back to the screen. i tried to turn it back on while in the game but it switches off automatically...

so i tap the home button, try to turn on airplay from the home and it works. but after a few seconds, it turns off by itself again.

so now i'm a bit confuse what exactly is the problem... is it my router or apple tv or an iphone 4s problem?

any help would be great, thanks.