When choosing the chain for a boundary there is a random end point on the spline? There is no reason for this i.e. no join in the spline, plane, etc. I have tried redrawing the spline a couple of times and the end point changes.
One suggestion is to change the control points. Sometimes you can make 2 control points from direction #1 join a single point in direction #2, thus eliminating a point from direction #2. This may help you out.
Also, changing the boundary conditions, to perhaps tangent, will remove a mystery endpoint.
It could also be just one of those cosmetic things that Pro/E puts in. When you shade the model or do an analysis on the surface, it really is not there.
Yep - tried that. Split it into 4 segments. The first 3 boundary surfaces worked ok then the last one had the two point I had placed on the curve where I split it, and again a random end point. This was stopping me from selecting a chain that I could trim.