Hey gotelin, sorry for the late answer. But the model of yours that used skin helped us find a big bug with the skin exporter which is now fixed (took some time, it was hard to nail down). So now all models with skin modifier should export flawlessly (once we update the plugin pack). About your physique model, i found it to be corrupt..as every other model i try works exporting just fine, and your model has some weird bones floating around .. which would cause the NAN float 0 somehow.
I recommend re-rigging the physique model.
The plugins update is coming shortly, it will be a nice update with several fixes for people!
