Hello Horst,
Thank you for the clarification.
Perhaps, the issue might be caused by the Host settings or some other file in the installation folder being somehow damaged by some antivirus/firewall software activity. You can try completely uninstalling the Host completely along with cleaning up all the remaining traces of the program as described in
this guide. After uninstalling Host please restart the remote machine and then try installing Host once again. This time after installing Host please also make sure to add its installation folder
C:\Program Files (x86)\Remote Utilities - Host\* to the antivirus/firewall software exception list if you have any installed.
Here's a guide on this that might be helpful.
Please let us know if the issue persists.