Unreal .psk/.psa exporter

The .fbx exporter to UDK seems to be working fine. I was curious as to another option for animation exports with the .psk/.psa. Does this exporter work? I get an error. Number of meshes: 1… Number of meshes <selected>: 1 Armature bones: 4 Mesh Vertex groups 0 doesn’t match. Not sure what vertex groups have to do with this???

I think that you must associate a vertex group to the bone.