You may not have been able to register with your selected username, if your username falls into a couple of categories.
These categories include names that imply administrative or official roles, obscenities, as well as the names of currently living Disney individuals. This also includes the primary names of Disney characters, including Mickey Mouse, Minnie Mouse, Goofy, Pluto, Donald Duck, Winnie the Pooh, Tigger, and Eeyore. Variations on these character names however, are typically permissible.
Names of famous deceased Disney personalities may or may not be approved, and will be handled on a case-by-case basis.
In addition, you may not use the full names of MousePlanet staff. Variations may or may not be approved, and will be handled on a case-by-case basis, although names that refer to MousePlanet or its staff in a derogatory manner will not be approved.