A couple of things I noticed in this model:
first, do you really want to shell the rails/legs of this thing? One thing you can do is split those off into a separate body, do the shell, then add them back in later. But, in this case, I think the real problem is the geometry on the domed end. If you turn on a curvature analysis map, you can see that the middle of that face has extremely high curvature:
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This will absolutely cause shell problems. Areas of high curvature will produce self-intersecting offset faces, which will cause the shell to fail. Even more important, though, is that there is some bad geometry inside your model. If you do a section view, you can see that there is a tiny hollow right at the end of that domed face:
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You can repair this by going into the Patch workspace, deleting these end faces, and the stray faces, and re-creating the domed face (first creating a sketch point at the dome top), stitching it all back together:
Jeff Strater
Engineering Director