Usernames are global to the entire SmartFile system. This means that once a username is taken on one site it can not be used on another. There are a few ways around this:
1) Use an email address as a username. As long as you don't have multiple user accounts using the same email address, this will work.
2) Purchase a realm. A realm allows you to have your own unique usernames outside of what exists already on SmartFile. Call us at 877-336-3453 to find out more about realms.