It will open .eps files no problem, but not .ai. (fonts or no fonts)
Posted this in another thread ("Acrobat PDF File Format is having difficulties"), and the only workaround was reinstalling 10 and resaving files as 10.

Since this also seems to have confounded this forum, can anyone point me towards an Adobe tech source that might be more intimate with CS and what may be causing this problem?

If I try copying the old file from 10 into a new CS doc, I immediately get an error message "Acrobat PDF File Format is having difficulties. There was a Macintosh system error (-37)" with AI10, and the ball spins for minutes (trying to paste into CS) without completing a paste.