Hi Sneather, you're running into "auto place" mode for the sweep being turned off. The way sweeping currently decides whether to turn auto place on or off is if the profile is contained within the bounding box of the rails. It basically assumes that if it is inside that bounding box then it's likely to be touching one of the rails and it will use the profile from it's current position instead of moving it to the start of the curve.

Also in addition to that auto-place mode is only activated if your sweep profile is planar and on one of the Top/Front/Right planes which your profile is not.

So to get this to work how you want, reorient your profile so that it's flat with respect to one of the view planes and then position it outside of the bounding box around those rails.

Also there seems to be some issue with your profile curve, it looks like a circle but it does not seem to be either closed (endpoints are slightly disjoint) or actually circular, you may want to just remove that and draw in a new circle profile curve on the x/y plane and make sure it's outside the bounding box around those rails and then do the sweep, see attached 3DM file for an example.

- Michael