I went into my profile and decided to put an Avatar on and tried to save it and I recieved the following error:
Not Acceptable

An appropriate representation of the requested resource /cgi-bin/ubbcgi/ultimatebb.cgi could not be found on this server.

I tried again a couple of times with the same error, I also tried it without making any modifications and the same error was produced. I am currently using Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.7.8) Gecko/20050511 Firefox/1.0.4 to browse the site.
Hope this helps!
GCS/E d- s++:- a- C+++ UL+++ P+ L++ E-- W- N+ o-- K- w--- O M+ V-- PS++ PE-- Y+ PGP t+ 5++ X+ R+++ tv+ b++ DI++ D--- G++ e+ h r+++ y++++