UBB.threads PHP Forum Software Community Forums UBB.threads 6 Version 6 Support Error: "You did not upload graemlin"

When attempting to add a new graemlin, I get the error "You did not upload graemlin!:"

The 'forums' install directory is set to 777
The forums/images directory is set to 777
The forums/images/graemlins directory is set to 777 as well.

Coincidentially, we can't upload avatars either.