I'm having quite a few reports from potential new users who are trying to sign up but keep being presented with with error message "Username may not contain the word" once they submit their details. I have just tried creating a new user and have found the same problem.
No idea what caused it, I reloaded the forum and it fixed it.
Do you know if you added a field to the username filter or the bad word filter recently and then deleted it?
I may have done a while back. I tried registering earlier and it didnt work, I'm now on my home PC and the registration using the same details worked. Great for now, but I have had quite a few of these problems. I'm going to try adding a few bad word filters to the list, as at the moment its empty so perhaps there's a null entry being validated somewhere.
Update: I've added one item to the username filter list, which was originally empty. Bad word filter now has one entry but is switched off. Fingers crossed