Ran into a problem today where no matter what I tried Open Source Broadcaster (OSB) would crash when trying to record anything in Kerbal Space Program (KSP). As soon as either I would alt-tab into KSP or start it up (both 32 and 64 bit versions of both) OSB would crash. It had worked for the past few days without any problem.
I finally read on of the crash reports and it seemed to be stemming from an unhandled exception in the graphics driver. I finally checked through my OSB settings and noticed that I had the resolution set for something larger then what my laptop screen was running at. Once I matched the currently running resolution everything seems to be working again.
TL;DR Check to make sure OSB isn’t trying to pull a larger resolution then what your monitor is running at.