I'm trying to upgrade from b4221 to b4550 but I keep getting this email when I try to upload the upgrade ISO in the web UI:

Uploaded file is missing or file is empty

I've redownloaded the file and checked the md5. The ISO is good. I've tried from Firefox and IE8. I also tried clearing the logs based on a post from a few years ago, but no luck. Is there anything else I can do to update my storage server?