"Illegal operand" - Can't open file

That error is a postscript error I believe which makes me think that the file was saved as an EPS file? The TrueType instruction leads me to believe that there's an issue with an embedded font.

CCC,

Many have, in different ways and succeeding in different degrees.

The message means that the file has been corrupted.

If someone recognizes the actual error in the code, it may be quite easy.

One thing often tried first is to create a new document and File>Place the (PDF contents, if any, of the) corrupted one to see how much may be rescued that way.

Fundamentally that is what Ray and Monica suggest. It will/may bring back the artwork to the degree that iti s represented in the (lower level) PDF version).

For a further recovery, you may go further:

Here are some websites where you can see whether it can rescue the actual file, and if it can, you may pay for a subscription to have it done,

http://www.recoverytoolbox.com/buy_illustrator.html

http://markzware.com/adobe-software/fix-illustrator-file-unknown-error-occurred-pdf2dtp-file-recovery/

http://www.illustrator.fixtoolbox.com/

http://www.erepairillustrator.com/

As far as I remember, the first one is for Win and the second one is for Mac, while the third and fourth one should be for both.

Here are a few pages about struggling with it yourself:

http://daxxter.wordpress.com/2009/04/16/how-to-recover-a-corrupted-illustrator-ai-file/

http://helpx.adobe.com/illustrator/kb/troubleshoot-damaged-illustrator-files.html

http://kb2.adobe.com/cps/500/cpsid_50032.html

http://kb2.adobe.com/cps/500/cpsid_50031.html

http://helpx.adobe.com/illustrator/kb/enable-content-recovery-mode-illustrator.html

It is always recommended to create backups with different names regularly, and to store backups in more than one place/way.

And also to save often.

If you have a CC subscription, saving files in your Creative Cloud Files folder will automatically create and keep versions up to 10 days.

https://helpx.adobe.com/illustrator/using/crash-file-data-recovery.html

https://helpx.adobe.com/creative-cloud/help/sync-files.html

https://helpx.adobe.com/creative-cloud/help/versioning-faq.html

and here are some other suggestions,

https://forums.adobe.com/message/9328988#9328988

Create a new file in Illustrator and place the corrupt file in it.

If the file opens in Acrobat at all, there's no need for an EPS workaround.

You might try opening in Acrobat PRO and exporting as PDF or EPS, then try opening in AI again. If it's a complicated file this may not be very helpful.