Some piece of registration logic is putting the disabled html attributed onto the button (thus disabling the HTML element in your browsers), possibly a piece of client side code which is not working anymore. I'm supposed to be the webmaster here and I could easily correct the problem however I cannot access the sites source code due to not having any FTP privileges.
For the time being PM me the details of the user (desired username, email etc) you'd like to register and I can do it from the admin portion of the forum, I have access to that at least.
P.S The culprit code is related to the agree checkbox, piece of js functionality which is supposed to re-enable the button needs urgent fixing.
He said eiher its been turned off or the file has been removed, whatever that means. I believe the server admin needs to take a look at it, not sure if a moderator could enable it or not.
Your friend is wrong, if the registration is turned off then the registration page should say something along those lines ex: "Registration has been disabled". Now if the actual PHP file has been removed then the manifestation would have been completely different, all of you would possibly get a white screen or some type of an error screen.