First of all, it is SmartSVN, not SmartGIT (which I however use as well) :-)….
I did indeed restart without any effect. Then I uninstalled SmartSVN, deleted the entire SmartSVN filer under programs, and installed it again.
Now I have shell integration working when SmartSVN is running. So far so good.
However, SmartSVN does not start up automatically when logging in. And I also really miss the SmartSVN icon in the Notification Tray, just hanging around in the background.