Insecure Connection error when using RealVNC Connect v8

When connecting to a remote device using RealVNC Connect v8, you may see the below error message:

Or this error message:

This message is shown when you are trying to connect using an unencrypted connection to a non-RealVNC VNC Server.

Please Note:

RealVNC has updated the v8 RealVNC Viewer so that connections to third party VNC servers is no longer supported.  If you wish to connect to an open source VNC Server, please download the appropriate Viewer from the open source VNC Servers download page.  

To connect, you will need to download and install RealVNC Connect and license the device on the target device.