The site has a lot of user numbers. As a result, you may need to get a little more creative with your user name selection. Try adding other characters before or after the user name you wish to use—many people add their birth year or other identifying information.You can only use letters and numbers for your user name; no spaces or special characters like dashes or underscores are allowed. User names are not case-sensitive, so 123ABC will be recognized as the same as 123abc. Therefore, if someone else has the user name you want but capitalizes different letters than you, you still can't create that user name.