Check your impedance.
The Architect and Director series amplifiers will run at 4 or 8 ohms. If you have a zone wired up in a way that puts over 8 ohms of impedance on the zone, over time it can go into protection mode because it is working too hard and it will overheat. The amplifier may work for a period of time, but ultimately it will shorten the life of the amplifier.
If the impedance is correct, the amplifier may be getting too hot due to where it is located. You want to make sure that the amplifier is located in a well ventilated area.
Director Amplifier Products Page
Architect Amplifier Products Page