Unable to connect to my workstations

I am not able to connect to through VNC viewer to my workstations. In the VNC server of my workstations I have this message:

Temporally disconnected from realVNC services

A networking error has prevented VNC Server from contacting RealVNC services.

VNC Server will reconnect to RealVNC services as soon as network connectivity is regained. If this problem
persists, re-register VNC Server or contact RealVNC technical support.