The files were on a disk in both OS's, but when booted in XP and starting MP, about 35.000 MP3's were deleted. That was the strange thing. When copied as winxp instead of MCE, the files remain when MP is started...
Why not all of them, very strange. Hope you can get to the bottom of this problem, i would definately monitor the folders. but as SteveV said there is nothing MP can do to mass delete 90% of MP3's.
Good luck finding the problem, but believe it cannot be a DRM issue (unless windows does not think you should have 2 copies of the same file)