Just to make that clear: This means that Samba/AD requires all connections to be encrypted. Disabling this (ucr set samba/ldap/server/require/strong/auth='no') allows plain, unencrypted connections again. So, if you trust your network, that might be fine, but please be aware that it lowers the security a lot.
The better solution would be if FreeNAS can be configured to use transport encryption (LDAPS).
Best regards,
Michael Grandjean