Why am I unable under settings/Airplay/Speakers to check the box?

During the middle of a movie streaming from Amazon via airplay tonight, the audio quit playing on the Apple TV. I went to settings on the Apple TV and the speaker box was unchecked for the Apple TV speakers. I am unable to check that box. All I hear is a thud. I have restarted the Apple TV. So I tested iTunes from my iMac to the Apple TV and it begins playing. Open to suggestions. I have seen other posts saying the Apple TV will only play audio on vides from Netflix but it played fine last night and for half of the movie tonight. Many thanks for your help.We only have one network and both devices are on it. Claudia