I wrestled with this problem for a while until I opened a JTAC Case on it.
Turns out that if you don't have the full Secure Meeting License installed then the LDAP search won't work no matter what you do.
This is a bit misleading since a limited number of SM sessions are allowed in the base licence, but they only work with manual invites. :/
On the other hand you can just purchase the SM License for about 7500$