problem making new accounts

Several of our users have had difficulties trying to sign up for a new account. The problem begins when they use short names (like chris or boba). They get an error message that says something like "must use only characters or numbers" (which they did, but I'm guessing the error was generated because the name was too short?).

Then they try to make another name, but only get the same error message. This error message often occurs several times. We have to close the browser down or use a different computer to complete the sign up process.

Any suggestions? (other than using a second computer)
assistemerso