Fix one RealVNC viewer problem.

I cannot connect to RealVNC server yesterday, the same today.
I did it on another PC. So the problem is in viewer, not in server.

Open regedit, find this:

HKEY_CURRENT_USER\Software\RealVNC\VNCViewer4\KnownHosts

and delete the server and reconnect, the viewer will generate a new secure key,
and then all is OK.