Thanks for the quick replay. I did some more research on the Nemesis thing and found a suggestion to set the executable to Win7 Compatibility. (Right click on "Nemesis Unlimited Behavior Engine.exe", select Properties, go-to Compatibility tab, check "Run this program in compatibility mode for:", select Windows 7, click OK.) It worked for me without needing virus exceptions.
Now, how brave do I feel to start deleting things from STEP patches in xEdit... May want to enjoy my nice shiny modern tested Skyrim a bit first.