In case this saves someone else some troubleshooting time, the recent SL 7.3 update of Samba from 4.4.x to 4.6.x can cause problems for legacy Windows 2000 clients (it’s a long story). Specifically, Samba 4.6.x inherits from Samba 4.5.x the change of the default value of the smb.conf "ntlm auth" parameter from “yes” to “no”. Servers that relied on the default value will need to explicitly include “ntlm auth = yes” in smb.conf. The fix is easy once the cause is discovered, but the breakage after a routine yum update was a surprise.
Regards,
Herb Thompson