I'll Tell you HOW I got there and maybe illuminate the issue for most of you as well.
MY C drive got full due to an errant Looping recursive process (NOT related to MM6) and while that process was running I was playing some MM6. MM6 then tried to write some files to that directory and could not, and as good programmers go failed and continued.
To the MM6 Teams - Once upon a time when hard disk space WAS an issue programmers checked for the error condition "DRIVE FULL" or maybe even the "SHARE LOCKED", or "UNAVAILABLE" then issue NICE messages like "WRITE TO HD FAILED" , I used the solution above to get my Heroes running again but find this a bad reflection on obviously good programmers (MM6 is no slouch of a program by any means!) to miss the simple things like dotting the i's and crossing the T's.