Cannot install any update

After removing the Cubase 6 trial, I had some issues with getting my Cubase 5 Studio back working.
I now can launch CS5 again, but any update fails.

So currently I have the default installation of the DVD and want to install Cubase_5.1.1_Update (when launching it says 5.1.2 … though) .

I disabled virusscanner/ firewall …