It is frustrating when I go to open a file previously saved in Illustrator CS5 and there is an error message reading file damaged. Or when someone emails an Illustrator file to me and the error reads file in unknown format. I use a MacBook Pro and Lion a little outdated but still should work right? Just a creative type and not a computer person any advice?
Nobody can know without seeing the files and knowing more about your saving/ storage/ e-mail procedures. Files don't corrupt themselves, there's always a technical reason like otehr tools opening/ inspecting the files and da,aging, the operating system indexing them for search right down to genuine hardware problems with your storage devices... Provide more info.
The bulk of email servers do not know what Illustrator files are and will often scan them for viruses. This often causes corruption in the file. Illustrator files should be compressed into a .zip archive before being emialed.