A damaged Adobe Illustrator file may cause an error or unexpected behaviour (e.g., crashes, objects failing to preview) when you modify, save, or print artwork in Illustrator. To determine if a damaged file is the cause, create a new Illustrator file and perform the same tasks that caused the problem with the original file. If you cannot re-create the problem with the new file, the original file may be damaged. To repair a damaged file, create a backup copy of it on your local hard drive, then look at these suggestions: <http://www.adobe.com/support/techdocs/11fbe.htm>
Here’s a couple of other ideas: Mordy Golding "Recovering Corrupt Files" 12/17/01 1:06pm </cgi-bin/webx?50@@.ef5b7af> and Help: Illegal Operand error. File will not open.
Another possibility is a corrupt graphic or font. Try a quick test by creating a new file with no PDFs, no graphics, just “This is a test” and a small box. Save it as C:\TEMP\TEST.AI. If that saves correctly you may have to review those items and maybe create a new file.