I have replaced an NT4 primary domain controller with a 2003 server. I still have an Nt4 server as an application server and as a Backup Domain Controller. It has been running fine until I add a new user that was never in the old domain.
Any new users that get added cannot authenticate to the NT4 server. All the previous users were already in the BDC when I change over. I cannot figure out why. I can authenticate as Administrator and any old users. I have sp6a loaded, someone said this would help, and have even added the new users to the Domain Admin group but still nothing. I cannot upgrade the Nt4 server as the application is an ERP system that is run throughout the company and I am told will not be supported in anything other than the NT environment.

If I add users on the NT first, it updates the PDC just fine but I still can't access the shares.

Any Ideas???

Rdb

Try demoting the NT4 server so it is no longer a DC and integrating it through DNS into your network.

Because your NT4 server is PDC, there is alot to do in order to keep the NT4 server as a DC and integrate it into a Server 2003 Schema AD network.
It is really not worth doing to be honest! Your NT4 server should run fine as a server, but not as a DC within your Server 2003 environment.

Also, you may want to consider scrapping that NT server and running NT in a virtual machine on top of a more modern OS/machine instead.