[Samba] Using Squid + Samba3 + Winbind

[STEPHEN W. COREY - 5535]

I've just setup a squid server using the above software. NTLM
authentication works 90% of the time with no user intervention. I'm
noticing that occasionally I'm getting a popup asking for a username and
password. I've looked that the winbind logs, and the only thing I notice
is:
 
[2003/12/17 14:38:00, 1]
nsswitch/winbindd_group.c:winbindd_getgroups(959)
  user 'root' does not exist

My user is MASTER\SWC, so I don't think I'm causing it. I also don't see
any errors regarding my username and/or authentication. I'm not able to
"cause" the popup to appear, so I'm not sure where to begin
troubleshooting... (smb.conf debug = 5 currently). If I do a "wbinfo -t"
it works fine, BTW.
 
Any ideas???