I'm assuming the vents are on top of the AVR and you need at least 3 inches of breathing room above it? Most manuals say 4 inches minimum so heat can escape quicker from the past AVRs I've had. Does it shut off every time you watch a movie? If so, try pulling AVR out and see if it shuts off. If it still does its the AVR itself that probably needs replaced down the road, if not then its the heat clearance issue. Looks like heat is escaping fine from looking at the pic but knowing myself I like more clearance.
Main theater: Sony 45es, 120 inch ST screen, Panny BDT500, Rotel RMB-1075, Rotel RSP-1068, Klipsch RP-280F, RP-450C, RP-160M, SVS PB13-Ultra x 2
Loft theater: Panasonic 60" plasma, Integra DTR-30.3, Axiom Audio M60, VP150, QS8, EP500