Steps to reproduce:
1. On new project, open player settings
2. Change Windows API to DX9 (top most)
3. Turn on VR support and add OpenVR to the list (priority doesn't matter)

Actual result: Play the project and crash
Expected result: Does not crash

Tested and reproduced on:
Windows 10
Unity 5.4.0b17

Not reproducible on:
Unity 5.4.0b11

Note: Could not test prior to 5.4, because VR option selection did not exist (it was only togleable, no switching between HTC Vive or Occulus etc)