Lion Server LDAP gone after restart - Error -14006
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.