The below message seems to be that the user account is corrupted in the backend. Please try with createsuperuser script OR repair database if you found this user entry in WMSDB.
Please use the following Community articles to resolve the problem.
How to create a super user:
How to repair the MySQL database:
http://community.cambiumnetworks.com/t5/Wireless-Manager/WM-4-0-Client-is-blocked/m-p/34919#M98