Go into the AppleTV menu and test the network- If that's OK, check with NetFlix to find out if the traffic on those programs is so high that this might be causing the problem.
Did you connect the AppleTV to the AVR or the TV? If the ATV is connected to the TV, why? If you're using eArc, how long is the HDMI cable and how new is it (meaning, is it current technology?)?