I am having similar problems. I’m using Rhynamo to import the outline geometry. The polycurves are all pointing in the same direction, closed, etc but I am getting the same error:
Error : Warning: Solid.ByLoft operation failed.
Unable to loft! : BAD_UV_SKIN_DIR — Surface U and V derivatives are in the same or opposite direction
I’ve rebuilt the polycurve by extracting each sub curve, getting its start point and then creating a new polycurve by points by the problem persists. Any suggestions?