In LdapAuthenication.php between lines 1490 and 1550 there are 4 references to $ldapconn which should be $this->ldapconn.
Alan Trick 23:00, 2 September 2010 (UTC)
Topic on Extension talk:LDAP Authentication
Wow. Good find. This code came from a patch. I haven't gotten the chance to fully test it. It definitely wouldn't have worked in that state :).
Fixed in r72741.