VR Preview Mode no longer working with HTC Vive in Unreal 4.13

I’ve noticed that VR Preview mode is greyed out and no longer accessible in Unreal Engine version 4.13 while trying to use my HTC Vive headset. I’ve run the engine as an administrator and that fixed the problem for one use of the software, but now its always greyed out. I’ve also opened up Steam VR separately as an experiment, and it works fine, and its worth mentioning, that if I then run The Unreal Editor as an administrator while Steam VR is left open, I can play my game in VR Preview, but with the Steam VR interface overlayed on top of everything.

And now its working again. I really have no idea why.

It sometimes happened to me but what i do is, turn on first the steamVR and then launch the project. Be sure your plugin VR is enable, just in case you did something with the plugins.

Just updated to the latest 4.13.1 and I have the same issue (the VR Preview is grayed out). Restarting everything from computer, then SteamVR, then UE4 doesn’t fix anything. The plugin is still enabled.
It’s working fine with the Occulus Rift.

EDIT: The log shows “LogHMD: SteamVR failed to initialize. Err: 105”
I confirm that creating the same project using 4.12.5 works without doing anything special