Surface loft gets split

I create a surface loft of differing cross sections around abend. When I export the surface as an IGES to be machined it splitsthe surface in two (like a clam shell) which makes more work forthe machinist. At first I thought it was because I was using guidecurves but I removed them and the surface still gets split. Whydoes this happen? How can I prevent it?

Thanks!SolidworksSurfacing