Max_2014 for x64: it supports vrscene scene files saved from max2014 software.
Max_2016 for x64 it supports vrscene scene files saved from max2016 software.
Maya_2015 for x64 it supports vrscene scene files saved from max2015 software.
Standalone for x64: It supports scenes that meets the standards of vrscence.
VR Standalone is relatively used by much less cliets, so we don't have all the versions of it installed on our renderfarm.
So it would be better to inform us in advance when a VR standalone user comes to render on our farm and we can install the proper version of the plugin for him.