I've had some problem, after deleting the NAS' account from the "Domain administrators" group (the sysadms didn't want me to have an admin account on the domain... :) ) So we tried putting the NAS account into a simple users group to see if it was working or not :

[...] winbindd[12332]:   unable to initialize domain list

...so everything was broke, Active directory service won't start anymore, no access to the CIFS share...

I've managed to make it working stopping the CIFS service, then I ran an "net ads join" and restarted the CIFS service... weird :P