Error 15401 adding login to SQL Server

I have a SAP Server running SQL2000 on Windows 2003.
Recently I migrated the server from a NT4 Domain to a AD Domain using
ADMT (with SID Migration for users) and everything seems ok.
Now, after one month, I have to shut down the old NT4 domain and before
doing it I have to replace the old logins in SQL with the correspondent
users in the new domain.
I applied a script which returned Error 15401: Windows NT user or group
NEWDOM\User not found. Check the name again.
I checked the KB article 324321
http://support.microsoft.com/default...b;en-us;324321
I applied the suggestion to verify if
SELECT name FROM sysxlogins WHERE sid = SUSER_SID 'NEWDOM\User')
returns a row, but this is not happening.
Then I tried to create the new login from the Enterprise Manager. So I
browse for the user and I'm able to find it (It exists! It's the same
user I use to login on the server) but when I apply the changes I get
the same 15401 Error.
So it seems that the KB article is not useful because:
1) There is no duplicate security identifier
2) It's not an authentication failure because I can login and browse
the AD. Also if I choose another AD user it works!
3) I don't think it's a case sensitivity problem because it happens
also from EM. By the way, I verified the SAMAccountName AD property of
the user and the name is all UpperCase.
I checked lots of posts dealing with this matter but they don't seem to
apply.
Any help would be greatly appreciated
Thanks
Dave
This post suggests that if all else fails, you may need to reboot the
server to refresh its locally cached credentials:
http://groups.google.co.uk/groups?hl...xa06 .phx.gbl
If you've already done that, then I would consider calling Microsoft -
if you've exhausted other resources, it's probably going to be the
fastest way to resolve the issue.
Simon