I get the error while setting up an ODBC connection on the client machine. It is:
Connection failed
SQLState 28000
SQL Server error 18456
Login failed for user 'domain\username'

Once the user is added individually, I can add the datasource with no problem. I have tested the authentication with SELECT SUSER_SNAME() and it does return the domain\username. SQL is running on a standalone server as a member of the same domain. It is an upgrade to a 6.5 installation.

Thanks.
John