Beginning with the release of Security Server version 9.52 (2010305) improved performance for cross domain authentication is available between two or more trusted domains.

When using Directory Services as your preferred Guest type, the Security Manager can now be configured to validate your LDAP settings at startup.  This is typically enabled by default.  You can check the option in Security Manager under the Options>Program Options menu.  If there are any problems you will be notified at start up.

Any issues can be corrected by reviewing the Security Manager’s Directory Services Definitions.

Go to Directory Services Definitions>Directory Services, then when creating new definitions or editing existing ones, in the Credentials tab, use encrypted bind and be sure to append the user name with the domain.
User Name: domain\username

This applies to Security Server version 9.52 or newer.  This should improve the ability to authenticate to Host from Guests in different domains as long as those domains have a two way trust.