UltraVNC

Thank you for your answers YY and redge:
I am not sure what exactly I should check on those 5 locations. Because the funny thing is if this does not work from a specific computer of course what I test is if it works from a second computer (that used to work before). Just to be on the safe side ...

I am using UVNC SC for some kind of support for my family and friends. It works fine, so the configuration can't be the problem I suppose.

There is a rc4.key included in my VNC and also inside my support.exe and it works on most machines, but sometimes, for unknown reasons I get this screen:
http ...