Just been testing vMix but having problems.

I have a Blackmagic Ultrastudio Monitor ( thunderbolt) that is plugged into my Blackmagic ATEM TVS vision mixer, I'm using this as the output from my computer. vMix is playing the video fine on screen but not outputting via the Ultrastudio. I know the Ultrastudio is working as I get output using Blackmagic media express. So I'm guessing it must be a settings issue, I'm SD widescreen.

Of no assistance, but I just avoid their products now. They might made some awesome other gear that doesn't involved interfacing to a computer, but the stuff that works with a computer is often close enough to working to completely frustrate you, but is so fussy will eventually drive you nuts thinking there has to be something easier :) I've wasted that much time with GoPros and BM Capture the best advice I could give myself is never buy BM Capture equipment. Since switching to alternative equipment my headaches just went away.