samba - Dec 2003 - Failing to store a SAM_ACCOUNT for [root] without a primary group RID

OK.

I've given up on using the 'net vampire' feature to suck our NT4
info.
Now I want to start afresh.

I've set the smb.conf file up, and run the script I found in the HTML 
docs to map common Windows Domain groups to unix groups. This worked OK.

Now I want to create a root account so I can actually join the domain 
from a Windows 2000 client.

When I run:

/usr/local/samba/bin/smbpasswd -a root

and enter the password I get:

tdb_update_sam: Failing to store a SAM_ACCOUNT for [root] without a 
primary group RID

I never used to get this under older ( 3.0+ ) versions. Something changed?

Dan