Viewing Free Busy times in Exchange 2000

Hi..We are currently going through a migration to E2K.. but I am finding that my Exchage 5.5 users are unable to view the Free/Busy data of those migrated onto E2K.. E2K can view back to 5.5….I have looked at the folder replication from E2K..and it seems to be in place.. but not replicating into 5.5….Any help is greatly appreciated.