Lion Server LDAP gone after restart - Error -14006 Similar to slapd daemon can't start but despite being accepted, the answer didn't really work for the asker. 

Shut down Lion Server 10.7.5 (on a 2011 Mini Server) today after Time Machine got itself in a tizzy and failed to backup for several hours while claiming it was "stopping" (presumably unrelated to problem, just the why of restarting it.)

Shut down hung - after 15 minutes or so I powered it off.

When it came back up, there was a red ball at the right of the username box with a nastygram indicating that network accounts were not available. Logged in the local administrative user - when trying to get to LDAP from workgroup manager "The node .LDAPv3/127.0.0.1 couldn't be opened because an unexpected error of type -14006 occurred" is the helpful, friendly response.

Server Alerts indicates self-signed certificates expired. Offers to repair/recreate. Doesn't seem to help. Reboot after that - still doesn't seem to help. Presumably the problem occurred at first reboot after they expired; That does not actually seem to be true however, looking at the expiry dates. Server has rebooted many times and LDAPv3 has been happy up until today.

This topic at AFP548 (first I've heard of that forum) seems related, but applying it may be difficult given that my self-signed certs are expired rather than removed.

It's going to be a late night trying to get my fileserver back in shape before other people arrive and want to use it. At least I have the files, but any better insight than that provided by the linked topics would be appreciated.
The moment LDAP and Open Directory get themselves into a tizzy I always look towards Kerberos.

Have a prowl with kadmin and ktutil and see if Kerberos is working nicely. Have a good look at getting your certificates A-OK. Check that DNS and reverse DNS are giving valid responses.

Copy the LDAP database then blow it away and start again to see if it's a problem with that. If slapd is up then try doing some searches with ldapsearch.