It's apparently a (random, since it only impacts a few people) crash during media initialization, and could be the result of a bug that LL just got fixed (here is yesterday's
commit to viewer-release).
The bug affects the winmm.dll provided with the viewer: I always wondered why LL bothered creating such a DLL at all, since there's a Windows equivalent that is normally installed with the OS itself...
Anyway, the fix is already included in next Cool VL Viewer releases. In the mean time, try removing winmm.dll from the Cool VL Viewer installation directory: the viewer will then resort on using the system's provided DLL, which could cure your crash.