Tue Jun 14, 2016 6:11 am by bob
Sounds a little odd, but, if you did not run the WIndow Layout Wizard when you added your second monitor, then that may explain it all.
When graphics drivers install/update or you add a new monitor, they sometimes change the internal display device names (the //./DISPLAY1 etc that ISBoxer shows in the WIndow Layout). The internal display device names are not the same as the Display Numbers that Windows shows you in the control panel (or your graphics driver software) If your internal display names changed through no fault of your own, then ISBoxer may have been trying to use a display device name which no longer had a physical device attached. This does do weird things. It has been noted before with one of the prior Nvidia updates a couple of years back and it caused a slew of FPS issues.