samba - Jul 2013 - getent passwd works but all wbinfo commands fail

I am seeing a bizarre problem on one of my machines.  The machine is 
running Samba 3.6.16 and is a member server in a Windows Active 
Directory domain.  getent passwd works just fine and returns all users, 
including users from the AD domain.  However, all wbinfo commands (such 
as wbinfo -t or wbinfo -u) fail with "could not obtain winbind interface 
details: WBC_ERR_WINBIND_NOT_AVAILABLE". winbind is running and I see 
nothing unusual in the logs.  Has anyone else seen this?

Thanks in advance for your help.


-- Moby