Be sure to check the "Unskinned Animated" export variable.
As explained on wiki
this needs to be activated for proper export of static objects that need to be animated or have bones. (Internally: it sets a bool (rigid=true) that's required to properly recognize settings during the granny import).
The error is unknown to us. It seems to just be an import issue in Maya due to the way your converter tool exports the tangents/bitangents you checked. If the object looks ok, I would not worry.