it seems like this lisp routine is broken.  not sure how to fix it, but it would be an awesome one to have in my arsenal.https://www.cadforum.cz/en/download.asp?fileID=722thanks.

nevermind.  you have to select a start and end point on the actual polylines, not out in space below or above them.

I don't have any idea what your real issue may have been, but just so you know, it does work as expected for me [in limited testing] when I pick "out in space below or above" the things I want to set to incremented elevations -- I don't need the points to be on them.[But it needs its description changed to be about what it really does.]