During installation if the Application Pool Name box is empty, you can specify an application pool name. This is an FQDN and must match the subject name for the certificate that was previously assigned.
Execute Get-CsTrustedApplicationPool. If the entry for Group Chat Server Pool shows Application Pool Name, different that subject name on any of the Certificates in the CA than we need to flag it.
EventID in the Event Log.
Install Group Chat Server.
At this step: http://technet.microsoft.com/en-us/library/gg398345.aspx
Enter an incorrect Application Pool Name.
Group Chat Server will be installed correctly, but no clients or Admin tool logins will work.