5a693e87_Plus__known_issues____RealVNC___Workaround
[ID] 243 [Description] VNC Viewer Plus cannot connect if the nodes in a Kerberos network environment are in different domains. [Status] Under consideration. [Workaround] 
Make sure the client computer, host computer and authentication server are in the same domain.
VNC® Viewer Plus (known issues) - RealVNC®
Workaround