According to Toyota's Camry repair manual, the main cruise light flashes five times when it goes into "auto cancel" cruise mode. This is a response to a failure of signal from speed sensors, actuators, or any other little thing that might come up. There should be a trouble code logged when this happens, but my ECU never seems to generate one.
I've had this issue for the last 150K with my 95 Avalon (out of 250K). I usually shut off the cruise, wait ten minutes, and try again. The cruise always works again after I park it and crank it up again.
I know - it's a dimwitted way to deal with the problem, but it only shows up every few weeks.