Hi Basj,
Today, I finally found the time to try your cleanboot suggestion.
I have created an new admin account. I need to mention here that this is a local account, unlike the "normal" account under which I reported the issues (that is a domain account). Then I logged in under the new account. Almost immediately I get a popup almost identically to the very first image in this forum post. The only difference being that it also says "To continue, enter an admin username and password" and it shows the domain name. Which is, under this local account, not desired. So I enter my username as computername\username and click yes. The result is again the same popup, this time with a red note "The requested operation requires elevation".
After clicking no to that one, I went to the Fences install folder, right clicked the executable and chose "Run as administrator" as that would in my opinion elevate the executable. I get the popup, try to log in with the local account, but I get the "requires elevation" error again.
Then I tried to login with my domain account and that did work. Unfortunately, the behavior of Fences is exactly as erronous as described earlier.
So, up to the cleanboot. When I try to open the msconfig application, again, I get the same issues as above: I get a popup asking for credentials, it refuses the local admin account (requires elevation), behaves the same when "run as administrator", complies when given the domain account.
Then I followed the instructions from the microsoft webpage, I kept the Fences entry enabled and restarted the computer. Almost immediately I get a popup almost identically to the very first image in this forum post. The only difference being that it also says "To continue, enter an admin username and password" and it shows the domain name. The local admin account gives me the "requires elevation" message, the network account works.
I do get the "Welcome to Fences" screen. Not while open, nor after closing does creating a fence work at all. Normally when I draw a rectangle on the screen, you can see it. Now, I don't and don't get the little poput "Create a fence" either.