"Imported some already processed files (P45 files in PSD format, done with CS3, No layers) and about 40% of them are being corrupted (?). The pictures turned into gray color as if they were in mask. "
Did you make sure that your maximize PSD/PSB compatibility, in your file handling preferences was on 'always?"
I had this problem with one older PS file, and when I re-saved with these preferences, it was fine.
laughfta