I saw a similar post here but don't know if it was resolved, however this is a bit different

Periodically I get an error box "object reference not set to an instance of an object" Underneath is "Unhandled"

If I try to send an error report or close the message pop up the popup keeps coming back.
The only way to get out of this loop is to shut down via Ctrl/alt/del

This can happen at any time. Today I had a static test card running while I was doing other things and when I came back to the computer the error box greeted me.
At another time I was outputting a video file and the error came up even though the video was still being output. Of course I couldn't do any switching until I had killed and rebooted vMix

I'm using an I7 laptop with Windows 8.1 and an Intensity Shuttle USB 3 as external output. Before the Shuttle I used the computer HDMI output and it did it there also.

Any ideas?

Alex

edit: should have said running version 13