Access Denied during login attempt

Attempting to log on to my Comcast gateway (Model DPC3941B) using cusadmin and highspeed user/pswd, but I get "access denied".

If I type in garbage for the password, it tells me I've used an invalid password. Even if the password is reset, is there something else preventing logon (it seems to know that "highspeed" IS the password, but is not allowing access.