I have a fairly large model that has been acting up lately.  The associated drawing takes forever (several minutes) to rebuild as it flickers between "Running" and "Not Responding".  The latest twist is that the model has suddenly become over defined.  I made no changes to the mates, I just opened it up and bam, red and yellow splats everywhere.  Most are over-defined mates, some are dangling relations.  Sometimes if I go to edit the mate, don't change anything, then close it the over-definition goes away, sometimes not...  I really don't look forward to spending the rest of the day repairing the darn thing.

Does this happen to anyone else?  If the file somehow got corrupt, is there a way to diagnose/repair/purge the thing?