Sadly, win_shell is not the entire solution.
After we thought it worked, we hit another Problem. A Microsoft Expert tried to fix it and figured out the following:
The Remote Registration only works, if the User had before an Interactive Login. So, the moment you delete the User Profile, the same Error appears. Login with the User and run command (remote) again, It works,
So, no real solution yet, maybe the Problem can be resolved in Checkmk by using the Local Certificate Store:
But that’s just my Idea. Since the Problems seam to be that the one for the user can’t be created.
Also, it would mean (I guess for all) that when the User (profile) of the Registration Users is removed, the Agent will stop working. (In the test, when removing the profile, the agent_ctl.exe status also shows the same error after).