Better check what is set on the metabase. I would guess somehow the
NTAuthenticationProviders metabase key has wrong values.
Open a prompt and type:
# cd c:\inetpub\AdminScripts
# cscript adsutil.vbs get w3svc/NTAuthenticationProviders
If you find you have something like "Negotiate,NTML" then type:
# cscript adsutil.vbs set w3svc/NTAuthenticationProviders
"Negotiate,NTLM"
or delete the key, since IIS6 has this value by default
# cscript adsutil.vbs delete w3svc/NTAuthenticationProviders
By the way, you should probably check it also on the specific WebSite
where the service is setup, example:
# cscript adsutil.vbs get w3svc/1/ROOT/NTAuthenticationProviders
IIS6 already has "Negotiate, NTLM" by default.
http://support.microsoft.com/kb/215383
Tiago Halm