How to Solve the “Unable to connect to VNC Server using your chosen security setting.” Error on VNC Connection Attempt
When you are trying to connect to Gnome’s screen sharing feature with a VNC client, if you get this error message, disable the encrypted connection setting with:
gsettings set org.gnome.Vino require-encryption false
Note: VNC is not a secure connection, even with encryption, unless used with SSH tunnelling! Encryption only encrypts the passwords sent, it does not encrypt the traffic (source).