Hi Jörg, I've attached a 3DM file for a version that is joined into a solid, I untrimmed and retrimmed various pieces to fix some of those structural problems that I showed above.

It should now import into 123D for you, and you'll probably have some better chance of getting the fillet done over there - you'll likely run into some problems filleting that area with MoI because I think the various pieces are meeting up at some slight shallow angles to one another rather than being smooth to each other.

I think some of the parts that look like arcs are connecting together not by the arcs endpoints but by some point inside of them, that makes for a very slight shallow angle between the pieces and MoI's fillet engine tends to have problems with such shallow angled pieces.

Here's an example of one of those shallow crease areas:






If you had those pieces meeting up more fully smoothly to one another instead of with just a slight few degrees crease between them it would have a much better chance at being filletable in MoI's fillet engine - it tends to be pretty sensitive to this particular kind of situation of things meeting each other almost smoothly but actually being a few degrees off from actually being tangent to one another.

Anyway I hope the attached solid 3DM version is helpful for you.

- Michael