Hello,
I got the same error message when installing OCS and mediation server on two Windows 2008 servers.
When I tried to configure my mediation server, I was not allowed at first.
Then I ran the next step in the setup process (certificates) and after that I could
go back to my OCS Server config tool and right click my mediation server and select properties. After configuring the two first tabs (General and Next Hop Connections) my mediation server could finally be started.
You can also use wbemtest.exe to query:
Select * from MSFT_SIPMediationServerConfigSetting
then at first you see the property blank (null), but after configuring the values shoud be there.
or the OCSGetWmiPropertyValue script from the OCS R2 resource kit:
cscript OCSGetWmiPropertyValue.wsf /wmiclass:MSFT_SIPMediationServerConfigSetting /propertyname:ProxyNextHopFQDN
/mk