that did the trick - so for anybody having the same problem ...
uninstall last beta, uninstall Workstation , uninstall ViClient 5.1
then reboot and manually fix the registry permission for HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\VMware, Inc. and HKEY_LOCAL_MACHINE\SOFTWARE\VMware, Inc.
After that reinstall Workstation, Converter and ViClient.
At the Converter-deveopers: dont worry - I think Converter is innocent. I rather blame the installer of WS 9 which is by far the worst installer that I have ever seen coming from VMware