Hi,
this error appears because you configured the users and cheked the federation box and in the forest level federation is disabled.
As you do not have an edgeproxy it does not make sense to configure users for remote access and federation. There are 2 possibilities
1. Reconfigure the users and uncheck the setting for federation
or
2. enable federation globally
- Open OCS Management console
- Right Klick on the Forest and choose Properties / Global Properties
- Change to the federation tab
- check the box "Enable Federation and Public IM connectivity
- The error should not appear
Hope this helps
Regards
Athanasios