Server 2000 and trust

HI

I am trying to setup a trust between a 2003r2 server and a 2000sp4 server.
I can create the trust via the 2003 box fine, and the trust verifys
correctly from the 2003 box.
however on the 2000 server when trying to verify the trust it gives an
"access denied" error after entering the username/password.
It is definatly hitting the 2003 box for authentication as if you put the
wrong password in you get incorrect username/password instead of access is
denied.

I have tried to use netdom to reset the trust, but that also comes back with
an "access is denied" error message.

I have successfully reset the secure channel on both servers and that made
no difference.

Both domains can successfully setup and verify a trust with a test domain i
setup to try and find which side was at fault.

I just cant understand why the 2003 thinks everything is ok, but the 2000
server cannot verify the trust.
all uses are domain admins so it isnt a permissions issue.

Any help on this will be greatly appreciated as i am tearing out my hair.