HI Manfred,

The issue seems to be due to some .dll file corrupted. I would suggest you to run SFC scan.

1. Press ‘Windows + X’ Keys.
2. Click on ‘Command Prompt (Admin)’ to bring up an elevated command prompt. 
3. In the command prompt type in the following command and then press Enter.
4. Enter the command: sfc /scannow

Also try the below points one after the another:
1. Sign out and Sign in
Sign out and Sign in or restart your PC and see if the problem goes away.
2. Automatic Repairs
If your PC prompts for Automatic Repair, continue with it and let Windows carry it out.
3. Kill and restart the Cortana process
If you find that Cortana is not working properly, the best thing to do would be to kill Cortana process and restart the process via Task Manager. If it was a minor runtime error Cortana would just take a restart to fix it.

Another temporary workaround that is creating a new user account.
To do this you’ll need to press Win+R then type in control panel.
Now select User Accounts>Change Account Type>Add New User in PC Settings.
You’ll see a couple of options that that allow you to add users to either your Family or just General use. Set one of these up and see if that solves the problem.

I hope this helps.

Regards,
Lokesh