This indicates an endpoint (typically the host computer) was reached by the connection attempt, but that no service was running on the relevant port and hence the connection was refused. Commonly, this is because:
- The service is not running.
- The service is not running on the port you contacted.
- The internal IP of the VNC® Server has changed, invalidating the port-forward rule in the router.
You should ensure that the service you are attempting to connect to is running correctly.
To resolve this error it is then suggested to follow the steps in Timed out waiting for a response from the host computer, and How do I connect to another computer over the Internet?
Note: An older cause of this error can be: when the machine is very slow, the UI process exits with a MsgBox if it can't connect back to the server within one second. This happens without any connection attempt to VNC Server from VNC Viewer. This issue is fixed in VNC 5.0.3.