SPNego Not working

Hi,

We are trying to implement SSO with Windows Kerberos to NW04s (SP 12) Java stack. I have pointed the UME to AD and then ran the SPNEGO Wizard successfully. I have configured the fall back mechanism as basis password authentication. Now When I try to login, it is still asking for the username and password. I dont see any error messages in the log. How do I disable the fallback password authentication mechanism ? Plz suggest.