I think the easiest solution for this would be disabling the intel or nvidia card completely and only using one. Not sure if your BIOS allows you to do this.
Otherwise bumblebee and hybrid cards in general are still very hard to get working completely.
Do you happen to know if the second connection (btw. HDMI, DVI, Displayport? What is it?) is connected to the nvidia or intel gpu?
Also the above error sometimes happens when the monitor is malfunctioning. Have you tried plugging off all cables and reconnect them again?
When connectring the second monitor please also execute
in a terminal to see the useable outputs