Black Screen on DK1, not on Debug HMD

I've been working on a game for VR, although I have no development kit to test with. I recently upgraded to the 0.4 SDK, and sent a copy of my game to someone who owns a DK1 for them to test. They see the Health/Safety Warning, but after that everything goes black instead of showing my game. In comparison, when I use "ovrHmd_CreateDebug" on my machine, everything works great (including distortion rendering).

We are both running Win 8.1 64-bit, have the 0.4 runtime installed, and have 780 Tis.

I'm using a custom-modified GLFW library with libOVR integration. The relevant source is here:
https://github.com/anprogrammer/node-glfw-ovr/blob/master/src/glfw.cc

At launch I call:
1. Init
2. EnableHMDRendering

For each frame I call:
1. StartVRFrame
2. Bind the render target
3. Call StartVREye, draw eye 0
4. Call StartVREye, draw eye 1
5. Call EndVRFrame

Any ideas are much appreciated.