I'm on a Mac and never have problems with Maya stuff- I always drop the entire runtime file I've downloaded onto Mac Converter before I install even though it doesn't affect jpg.s ....... I too think a more careful wording of your problem would have been a good idea - Studio Maya has released some of the best free stuff around, mac or pc !. Have you tried opening the texture files in an image editor to check them that way ? Are you using the most recent version of Stuffit ? It does sound like it may be an un-zipping issue to me. Its the first thing I'd check out. Is it only Maya files ?

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