OCS - There was a problem verifying the certificate from the server

I have recently experienced an issue with Instant Messaging (IM) after the user and computer migration.  A few users were not able to logon to the Office Communication Server (OCS).  There were getting the following error message:

There was a problem verifying the certificate from the server.  Please contact your system administrator. 

We resolved this issued by installing the root certificate in the trusted store of the local workstation. 

Posted in: Messenger for Mac,OCS,Office Communications Server