OD Master, PDC on OS X, Windows Boxes can not authenticate

We have our OS X Xserve running 10.4.11 being our Open Dir master as well as a PDC for small windows domain. We have successfully joined windows machines to our domain, and can even log in using our LDAP info. At random times, we can not log in with out LDAP info to our Mac or to a shared drive on a Windows 2003 server. Looking thru the SMB logs on our Login Server, I am seeing [i]/SourceCache/samba/samba-100.9/samba/source/nmbd/nmbd.c:terminate(56) Got SIGTERM: going down... [/i] error in the Windows Name service log. It appears that when a windows service/user tries to authenticate, sometimes the domain controller is available and sometimes it is not. Any tips on how we can have our users use their LDAP info to authenticate to a windows machine?