You can add a server behavior to make sure the user name entered is not taken by another registered user.
The Check New Username dialog box appears.
For instructions, see Setting the Check New Username dialog box options.
Dreamweaver adds a server behavior to the registration page that checks that the user name submitted by a visitor is unique before adding that visitors information to the database of registered users.
When the user clicks the Submit button on the registration page, the server behavior compares the user name entered by the user against the user names stored in a database table of registered users. If no matching user name is found in the database table, the server behavior carries out the insert record operation normally. If a matching user name is found, the server behavior cancels the insert record operation and opens a new page (usually a page alerting the user that the user name is already taken).