"File.ai is unkown format and cannot be opened" error while opening files in Illustrator 2015

Hi there,

Thanks for reaching out. I hope your issue is resolved by now. We'd appreciate if you can share the solution with us here. It'll help other users having similar concern.

If you still have issues, please share information asked by Monika in earlier response so that we can understand your issue better and assist accordingly. Looking forward to your response.

Regards,

Ashutosh

Did you update the system recently?

Did you install any third party plugins?

When was the last time you could use the file?

It's absolutely possible that files go corrupt. I haven't seen that happen to my own files, but it happens. Where did you save the file?

Being unable to open files or to create new ones is often related to a missing printer. But usually in that case Illustrator crashes and doesn't show this kind of messages. But of course that is something you could investigate: set up a PDF printer if you don't have a physical one.

I suppose you already restarted the system? Reset the Illustrator preferences?