Cluster Problem

I just want to ask about any issue that i have with an CTS4000 PBX.
Everything was functioning just right with a th PBX untill yesterday.
While i was checking out the status of the PBX at the twinstar status
found that the cluster have a problem and the first server is unreachable.
i checked all the settings on the unreachable server but didn’t find any problem.
The hardware does not have any issue and is functioning just fine.

Any ideas?

Thanks in advance.