“Oh no! Something has gone wrong” message is all what you get when you VNC to Gnome 3 in Fedora 20 on a box without any physical monitor attached to any of the video outputs with enabled autologin and screen sharing (vino). There is an error in /var/log/messages ‘TypeError: this.primaryMonitor is undefined’ at /usr/share/gnome-shell/js/ui/layout.js:410. I haven’t found a Fedora bug open for this.
You cannot also simply configure e.g. tiger-vnc because of other two bugs, one closed and one open preventing login screen from entering the password – as somebody would be pressing the entry key on and on.
I was not able to find a straight and simple fix unless I’ve hit this solution for Ubuntu, and ported it to Fedora 20:
You can then VNC to port :0 and you will be logged in directly without a need to enter the user password. I suggest SSH tunneling.