After much time lost trying, I think it's time to give up and just build a new tank. Your suggestion that Carrara was confusing the two documents sounded really good, so I renamed the tank, renamed all the moving parts and tried again. No movement. Then I went back and moved all the keyframes forward by one frame, so all renamed parts are now in a different position. No movement. Then I imported the tank. The treads looked OK, but the rest of it was a scrambled mess. [there was keyframe info on the treads, however] Then I exported it as an .obj, and re-imported. Now there was no keyframe info, all the names had been abbreviated, textures gone...another fine mess. Time for a new tank...from scratch.