When adding a user avatar the upload often fails, even though the avatar image meets all requirements.
The last failure I have seen personally was with a 'gif' file, with the required 50x50 pixels, and 2Kb in size.
It refused to upload.

Changing the file format to 'jpg', with a slightly larger Kb size worked ok.

Any ideas?

Could you repeat this on miniBB demo?

I'm not sure if GIFs are allowed to upload at all. At least they are disabled in the most recent default version.

All in all, if you are using the latest version of this add-on, I've introduced the malicious PHP code rejection, if it's found in the uploaded binary. May be it could cause something... not sure. If you could attach couple of files, which do not pass, to our FileBank, I could take a closer look.

In any case I'd suggest you increase the maximum file size as the average Joe doesn't necessarily have skills to make sure his file size is within the limits. That 2 kilobytes is so easy to reach even for 50x50 file.

Ooops, it was a gif, with the latest code!

My mistake!!!

... :)