MyBB Community Forums

I recently set up a mybb forum for the first time. Everything is going well and working, except adding an avatar. If I choose a file that is the size 100x100 and smaller than 25kb I get the error "The file upload failed. Please choose a valid file and try again. "

I have changed the permissions (I am running a Debian server) for the uploads as well as avatars to 777, but to no avail. One friend was able to get the avatar to the server, but it doesn't show, and any further attempts won't work at all.

Thanks in advance,
Freece