Illustrator 10 - crash on save

Hello, I am using Illustrator 10 on Windows XP. Occasionally (this has happened several times in the past), when attempting to save a file in Illustrator native format, Illustrator chokes, and has to be shut down. Now, when this happens, I have a couple options. I can save the file as pdf or eps, no problem. I can also save as Illustrator native, as long as the "create PDF compatible file" box is unchecked. But if that box is checked, the program hangs.

This does not happen to all files, only to some. Maybe once every 2 months. Sometimes they are imported from somewhere else (Flash, Freehand, Linux), sometimes they were built in Illustrator. Fonts and preferences do not seem to have anything to do with this.

So it isn't posing any real problems, since it can be easily worked around, but I am very interested in knowing exactly what is going on here. I think that the "create PDF compatible file" has more to it than Acrobat interoperability.

Thanks in advance for all comments.