LDAP initialization failed

Our LDAP server stopped working a couple of weeks ago for no apparent
reason. This stopped iManager and iFolders from working as well. I ran
pkdiag and it found two out of date certificates. I used pkdiag to fix
this and restarted the server but the problem persisted. I am getting
error messages on the Apache screen of our server console stating
that "LDAP initialization failed" and "Can't contact LDAP server(81)". I
have re-exported the SSL CertificateDNS object to
sys:\public\RootCert.der and restarted the server but still nothing. I
have tried LDAP authentication using a LDAP browser with anonymous and
authenticated authorization on ports 389 and 636 but it failed. I would
appreciate any suggestions.