The only thing that helped was a hard reset.
( turning off the PC and restart it.)

Possible cause, things i notice:
When I start VS I always let VS create new empty document.
On the installation procedure VS asked if I wanted to save
this document. Whereas the new document had no content
and I did nothing to it myself.

At the first try a box appeared with only four buttons.
At another try a box appeard ask if I like to save the document.

The solution i found:
I closed the empty document before i triggered the update.
That went without any problems.