Error message at Sign up page
One user is trying to sign up at my site using the string "PEWM" at field "User", but the site show him the message bellow:
<strong>ERROR</strong>: This username is invalid because it uses illegal characters. Please enter a valid username.
What's going on? Is there a bug?
I'm using Wordpress WPMU 3.5.2, Classipress 3.3 and Advanced Custom Fields for ClassiPress.