The connection between Apple TV and AirParrot sometimes needs to be reset, because there is a problem with the sound. This seems to happen more often if you are switching back and forth between showing content from an iPad via AirPlay and a computer using AirParrot—however it is a known issue, and can happen at any time. The easiest fix is restarting the Apple TV (outlined below). Although the restart works in a large majority of cases, doing a full restart on your computer may help if the Apple TV restart did not work.
A printable version of the document is here: Air.parrot.sound.issues.