Surface Blending - Unexpected pinching

 From:  manz
1546.2 In reply to 1546.1 
The main problem is the fact you have such a small model (only 20 unit long) so the calculations being made are passing MoI limit. (there are crossing control points on the blend)

I just went to your first stage, deleted the sweep, then scaled the model up (X50) remade the sweep, then boolean, then blend. The finish was then OK.