Unable to Upload Avatars (Resolved)

I'll just edit this since it wasn't PunBB's fault.

If you receive a 503 error when uploading avatars, your host may have mod_security enabled. It will look something like this:

503 Service Temporarily Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

The resolution is to disable it using a .htaccess file from here:
http://www.vbulletin.com/forum/showthread.php?t=197290

Regards