most probably, you’ve set VNC to SSL enabled and use a selfsigned cert ?
If so, this is your solution: Help:VNC Failed to connect to server (code: 1006)
go to: https://<SUNSTONE>:29876
(replace <SUNSTONE> with ur IP or url)
if you use a selfsigned cert, you should get a browser warning, accept the cert, try again.
Or disable SSL for VNC in oned.conf