[This post|http://lists.samba.org/archive/samba/2005-January/098470.html] helped a bit. 

  

 ~EwenMcNeill: From what I can tell the underlying cause of this error is that the authentication of the user worked, but it wasn't possible to load in their account information. Not having set up nsswitch.conf properly is one cause of that; having set up nsswitch.conf but not having restarted nscd (the caching daemon) is another cause. (The most obvious symptom for "not having restarted nscd" is that "getent passwd | grep USER" finds the user, but "getent passwd USER" doesn't, because the former doesn't seem to go through nscd, but the latter does -- and the latter is the same sort of call as Samba is making. If you see those symptoms check for nscd even if you didn't think you had it installed.) 

  

 Another thing to check (esp on Solaris) is that the libnss_winbind.so is in /lib and there are a bunch of symbolic links to it in /lib: 

  libnss_winbind.so.1 

  libnss_winbind.so.2