Red light went on on one of my Ayre MX-R amps

One MX-R owner's manual, coming right up.

Ayre is pretty cool about having lots of information on-line.

MX-R owner's manual

FYI, calling Ayre is another good idea, as they are VERY helpful!

Good Luck!

please post your findings as I have the MX-R and I am curious.

Read through the manual and the red LED indicates DC on the amplifiers incoming signal.
If it has never happened before do not worry about it. the sort of device that checks for it is very sensitive, and may have just had a 'cosmic ray' hiccup. Or something like that. Poltergeist activity is also a possible reason, if the cosmic ray seems too far out.
Anyway, don't worry be happy. If it happens again, do the same thing. If it starts happening all the time, THEN worry.

Liz, LOL!