Please remember that all degree seeking students are required to obtain advisor approval before registering online.
Most errors will provide an explanation for the error. Before attempting to register check to make sure you have no active holds or restrictions on your account which could prevent you from registering. Active holds will be associated with a phone number for you to call to inquire about how to have the hold removed.
If you still have an error after verifying that all restrictions/holds have been removed, please contact your advisor.