Hi MrGuzzi - yes like Pilou mentions you've somehow got a lot of duplicated copies of these surfaces that are stacked up on top of each other.

It can be a little difficult to see this since they are all stacked up in the same spot, but what appears to be one surface in your model there is actually like 10 identical surfaces all in the same spot.

So for instance if you click and drag on any of those surfaces and pull it away, you'll see that there is another one underneath, and then if you drag that one you'll see another one was underneath, etc...

In order to Join up properly you'll need to have just one surface in each of those spots, it looks like Pilou has posted a tuned up version attached above, thanks Pilou!

- Michael