Citing the
Mesh support paragraph of the features and screen shots page, "The Cool VL Viewer is also capable of uploading meshes (
for now only in the Linux and MacOS-X versions because of a bug in the compiler of VS2005 under Windows)."
Mesh upload will be enabled in Windows when I will gather enough courage and find enough time to migrate to VS2010 (which means rebuilding a Windows virtual machine from scratch, installing VS2010 and all the needed hotfixes, patches and whatnot to make it actually work, then to modify the viewer build system to compile under VS2010)...
Note that you can force-enable mesh upload on WIndows builds by setting the MeshUploadEnable debug setting to TRUE, but then, when uploading a mesh, the viewer will fail with a message telling the mesh failed to decode.