... ah ... i have all the stuff including boxes in the main Blender file, so at export i have to drag eaxh thing to 0.0.0. position ... doe, didnt do for this one as for testing out the importer thing (out of speed) ... ill reupload it centered and white textures right away ... also, can those collision meshes at the wheels stay as they are ? (it should now stand up properly when animated ... but still the enabling and disabling of wheels as in aircrafts would be needed, otherwise, it will still do some improper things).
As for that UFO - if im right its just like any vehicle - bad mass+bad gravity center+bad wheel-property mix. That allways makes them models froggy-jump.
That log just lists parts witch had an else texture-path selected in blender, nothing out of ordinary (have them at multiple places also as a backup policy ... just sometimes forget to re-point them, but has no effect on the final import when i modify the matlib file and add all the textures)
... here is the corrected file + textures :
https://drive.google.com/file/d/0B3ZscF0ox2AGQS1WZU9LSHlfQjQ/view?usp=sharing