I'm guessing you're attempting to pull in a fairly new version of an .ai file. We ran into this too. Around CS release of Illustrator Adobe completely changed how they handled text within their files. We even saw it going from Illustrator 10 to a newer version.
The best, but still not perfect, method is to save back your AI file from Illustrator to likely the oldest version you can. We've had fair results utilizing that method. If you have a large quantity to do you should be able to set up a fairly simple macro in Illustrator to a folder's worth.
