Well, the files (mentioned before) are in 2 or 3 differrent subdirectories, and so far I have not been able to find a pattern, since all file types were added the first time I opened MCE, and after that none has been added or removed, even though they files were removed from the hard drive on the other pc, or some had been added ...
Tried a trick with opening WMP, tried to update the library from there .. Did not work..