the new DeskApp Version works like a charm and solved the problem.
I think it was a graphic problem because i’ve tried the tip from @marty first and there were a lot of GPU errors in the log.
What version are you using.
I checked on this versions and it works as expected:
ii kopano-webapp-plugin-meetings 3.0.0.81 all Kopano WebApp Meetings Plugin
ii kopano-webmeetings 0.29.5-1 amd64 Kopano Webmeetings audio/video call and
or the integrated installer from w2012 TS? (btw withour R2?)
and please check if the *.msi-file has no flag set to unsave (right-click -> properties -> “Die Datei stammt von einem anderen Computer. Der Zugrioff wurde aus Sicherheitsgründen eventuell blockiert” -> click “allow” or “Zulassen” )
The last one got me some days to install exchange-Server update :)