There is a known bug in 3ds Max that affects kW X-port 1.3. If you do not collapse the modifier stack below the Skin or Physique modifier before you export, then 3ds Max will give kW the wrong vertex data -- it will export the mesh at the bottom of the stack. Thus, when exporting, your stack should look like this:
+ Physique
+ Editable Mesh
It should not look like this:
+ UVW Map
+ Physique
+ Cap Holes
+ Editable Mesh
+ Editable Mesh
Box
The easiest way to make this happen is to make sure there are no modifiers on top of Physique/Skin, and then right-click the modifier right below Physique and select "Collapse To." Also note that any modifiers found above Physique/Skin will not be exported (the UVW map, in this case).
If this is the problem for you, and you are a paying customer of 3ds Max (not just a trial user), I suggest you call up their support and ask them to fix issue number 1066627, which is the Autodesk 3ds Max bug number they opened for me about this problem. If nobody tells them about this, they will not prioritize fixing this bug.
Jon Watte, Direct3D MVP
kW X-port 3ds Max .X exporter
kW Animation source code