Thanks to Microsoft Australia’s Johann Kruse for bringing this to my attention.
The basics are
- No group chat on Windows Server 2008 R2 servers or in Windows Server 2008 R2 domains or forests. (expect a hotfix in April to support GC client & admin in a R2 forest)
- OCS 2007 R2 can only be freshly installed on a freshly installed 2008 R2 server – upgrading an existing 2008 server to R2 is not supported.
Of course, there is lots more to the article and there are detailed instructions on the hotfixes required as well as the minimum file versions so go check it out for the full details.