Username already taken

title really says it all but iv looked everywhere and there is no other username but mine
but the error i get when my friend trys to make an account *Sorry, but this username has already been taken.*

Hi!

It happens because of a security option.
Go to Administration Panel => General => Forum => Security => Security Administration => Unauthorize subscriptions made with the most commonly used spam usernames. : No.
Save.

Thank you good sir

Glad I could help.