We have 2 sites. Main site (site A) in which we have a DC, an exchange 2007 server, an OCS std and a mediation server and about 100 moc clients. A branch office (site B) in which we have only one server, which is a DC and 4 moc clients. Unfurtunately 2 sites are also on 2 different forests. Two sites are connected via VPN and 2 forests have trust relationship. I've created linked mailboxes for site's B users on exchange server on site A and I can connect to exchange using user credentials of forest B. This creates disables users on site A and syncronizes appropriete attributes. Also I syncronize ObjectSID of users on site B with ms-RTC-SIP-OriginatorSID on disabled users on site A. But I cannot login to moc client from pcs on site B using their credentials.