Can anyone give me a clue as to why this happened? This is constructed as a solid body and when I shell it, I get a thick wall on the lofted area.

I've attached a pic of the section view and the actual SW model.

Richard: it is absolutley with the loft. Originally I did a loft on one half of the part and then mirrored it, and that worked fine, it shelled it perfectly. But then I worked on some other features on the part, and it gave me errors and didn't allow the loft to be mirrored, so I remodeled with the left and right side as one....and this is the results.