...selection are unsupported by Adobe stock and hence cannot be uploaded

I get the message "all of the files in your selection are unsupported by Adobe stock and hence cannot be uploaded." when attempting to upload an illustrator file through Bridge. I also get an error when uploading directly to Adobe Stock. The problem, this message doesn't give me enough information to troubleshoot the problem. I have uploaded exactly the same way before, no issues.

Click on the Learn More link doesn't help.

Does anyone have a master list of items to check for? Maybe I can start there.