Your cage may not actually be exporting correctly to xnormal, make sure your mesh is triangulated first(drop an edit mesh modifier in your stack before export).
It happened to me a couple of times. From what I can tell this is specific to fbx. Try exporting out your mesh as obj, then putting it back and exporting an fbx.
After setting it up once, that's what it is now for me, a one click button to export all maps with the option to export only the map I'm currently working on as well.
Blender's .obj export script doubles the verticies dued. ;p export and then load it back in blender and you'll see it doubled i think Horrible 1st post hmm
Thats the problem! I can't export from Zbrush to maya...maya starts, but no model inside :( ...but I can export from Maya to Zbrush without a problem..