Can't execute package - Assertion failed


I’m having an issue when I try to execute a package I’ve been working on for some time now. I’m using the multi-user viewer template with my HTC Vive and everytime I try to Host a Session, I get this message:

Assertion Failed: !SteamVRHMD → VRCompositor
[File:D:\Build++UE4\Sync\Engine\Plugins\Runtime\Steam\SteamVR\Source\SteamVR\Private\SteamVRSplash.cpp] [Line:54]

Does anyone know how I could fix this problem and finally run my project?

Also, if I try to run it in Desktop mode instead of VR mode, it works fine.

Thank you in advance.