DFFD. Specifically for uploads of DF-related files.
Edit: I have another idea. Use DFHack to put an obsidian wall where you want the wall to be, then use tiletypes to change it to the layer stone.
Oh. Well now. You can do that? All hail the chainsaw of cheats+logic.
I had this happen not too long ago and the only thing that fixed the very most stubborn case (Armok knows why) was cancelling the offender and removing all adjacent tiles of construction, then building the offender first, then rebuilding the stuff that had gone up successfully before.
Yeah, that's the first thing I tried... Problem was, it didn't work. Natural stone to the NW, NE, SE, S, SW; blank space to the west, north, an' south. Dorf kept standing on top of the wall it was building, and then cancelling because it didn't move itself.
I have this same problem. The only way i know to deal with it is to BUILD EACH WALL SEGMENT INDIVIDUALLY over the course of months. Lotsa pausing and time wasting invovled. It is a micro-managment nightmare because i'm trying to build a wall on top of another wall and don't want to waste material to build a scaffolding.
I think somebody mentioned this was a bug and i hope to god that's right bcs, well who wants to build a wall 1 segmant at a fkin time. Walls are too useful for staff to ignore this bug.
http://www.bay12games.com/dwarves/mantisbt/view.php?id=5991
I have never, ever had this bug except for this one time, with this one tile. If this happened with every wall tile I would probably be out murdering things instead of posting on forums. D:
Removing the wall either west or south (or both) is what I've had to do for the really stubborn tiles.
I have not noticed an otherwise normal cancellation cause this kind of problem, however. Its always been either they stand on the tile and cancel, or they don't.
Melomel, you might need to just take a break from the game for a few hours. Known bugs can be frustrating, especially when they are inconsistently triggered like this one is.
Removing did absolutely nothing. Forcing the dwarves to stand on adjacent tiles and ONLY adjacent tiles resulted in them ignoring the half-built wall completely.
Quitting the game and restarting it worked... sort of. Sometimes they cancel construction because they're standing on the same tile as the wall-they're-building again, but a couple of times, they've completed the wall--but only, and I do mean ONLY, while standing NE of it. Is cattycorner (okay, ORTHAGONAL) construction a go in .11?