Recently I had to install Lync Server 2010 on a repurposed Windows 2008 R2 server within a lab environment. One of the issues that I ran across was preventing me from accessing the Lync Control Panel from the Lync Front End server.
Attempting to open the Lync Control Panel from the Lync 2010 Front End server displayed the following error:
I started by confirming that all of the prerequisites were installed, followed TechNet: Troubleshooting Lync Server 2010 Control Panel, and confirmed the Kerberos was configured and working properly. None of these changed the error.
In the end, the resolution was to enable the DisableLoopBackCheck registry key.
WARNING: This setting should be carefully considered as this can change the security of a server. This scenario was a lab environment with no Internet access. For production environments, you may want to consider using the BackConnectionHostNames registry.