Microsoft Office Communicator 2005 was not installed.
Information:
http://support.microsoft.com/default.aspx/kb/974571?p=1
ESX Cannot Find The Specified Host
(These instructions are for an ESX host that can’t connect, but has connected in the past with no problems. If it’s your first time trying to connect a host, it’s probably a simple solution such as a DNS issue.)
If you can’t reconnect an ESX host, SSH into your service console and restart the following services: