We have the exact same problem on MC 8.0 run on iMac 14,3 8GB RAM GEForce GT750.At least 5 out of 16 machines in one of our suites do that. I cannot pinpoint it to particural user accounts though, and the alert comes up as soon as MC tries AMAing the first clip.
Any hope would be great, tried AVID community so far now help.