I checked the files & they were not corrupt.
I think what might have happened is that I created the first part, a half moon clamp, with a right hand thread by using adaptivity from a shaft in the assembly.
Then I inserted a separate .ipt, which I created from the half moon clamp, but this part needed a left-hand thread.
Trying to mate the 2 caused the error. So I broke the adaptive features in both & dimensioned from their respective origins, then assembled the 2 using distance mates. Which is ok, but I would have like to kept the adaptive features is case, which always happens in new designs, the shaft distance changes. This way my parts would change on the fly.
My system is somewhat stable. I crash about 3 or 4 times a day. I need to have several different programs running @ the same time, this could play into the problem.
Thx for the reply Rich.