Is it the red over-exposure arrow after the "500" that's blinking and not the round red LED next the "B" in the viewfinder? If so, that doesn't sound good, as I think the only function of that light is to indicate over-exposure. On the other hand, the red warning light on the left in the finder (next to "B") is used to indicate a closed light shield, shutter not cocked, no film, no lens and/or weak battery. If it's that warning light you should check all those things. If it's the over-exposure arrow then I guess you could check if the film speed got accidentally changed to a high setting? Also, you could remove the lens and make sure it's seated properly and there's nothing interfering with the lens/body contacts.
In any case, try turning the camera off, taking the battery out and waiting a while before installing a new one. I've never had a problem like this with my Mamiya 7, but I've had a Nikon get a little moisture inside and temporarily screw up the electronics (until it dried out).
Sorry if this doesn't help, but could you keep us other M7 owners informed of what happens in case we have the same experience?