The attached save pertains to: http://www.bay12games.com/dwarves/mantisbt/view.php?id=5991

I've experienced the same problem with this brand new fort, trying to build a wall in a dug out staircase. This is a new world built in 34.11. Check the bottom of the stairs right next to the embark point. I immediately hit a cavern so I tried to build a wall. It doesn't matter if I delete it and try again; the builder just stands on top of the site, then cancels.

This build and save uses the LazyDorf repack uploaded June 5th, and the Mayday graphics set.