I'm with Markw on this one. It sounds like protection mode form a taxing scene. The fact that it's only during a specific scene would indicate that the load is too great for the receiver to handle.
Let us know about the scene in question. Also, what kind of speakers are you driving and how many total speakers do you have hooked up to the receiver. I wonder if a phase problem might be to blame? You might make sure you have your speakers in phase (positive to positive and nagative to nagative) for ALL connections to receiver and speakers. If you get them crossed, it could cause problems. Just a thought.
Also, you might try renting the same DVD and see if you still have the same problem. Not sure how, but maybe it's the DVD? I doubt it though.
Shinerman.