Way past my bed time but I looked at your model quickly, take a look at the control points on both ends of the extrusion center-line path (pink middle one on the rightside view in free form modeler). One end point has a curve handle & the other doesn't. This may be your problem. I didn't have time to look further, hope this helps. PS- was this created on a MAC or Windows? I'm on MAC & had no trouble opening this file.-Bye