so, for whatever reason, the guide stopped guiding it for a second and it caused an injury? maybe he had to dodge swings from a tantruming dwarf or something, it's one of many options
what message do you get when you try to make soap? It would really help if you gave enough information for us to help you. There used to be a bug with lye in buckets that also contained water. Do you have certain stockpiles set to only give (or recieve) to certain other stockpiles or workshops? Do you have any burrows? Even inactive burrows can mess with workshops. Have you tried assigning the job order through the manager? Sometimes the issue that prevents you from setting the job at the workshop is solved by using the manager.
The job shows up as red, listing the required materials. I have burrows, but nobody's assigned to any of them.
EDIT:
Using the manager worked, but they still show up as red. Odd.
to restate it, even inactive burrows, that is, with noone assigned to them nor active as civ alert, will mess up many workshops. At least one burrow that overlaps your soap maker does not include all the components you need to make soap. Something similar happens with smelters that can't 'see' ores that are outside (unused) burrows, for example when there is no stone stockpile, the smelter would just have to grab the stone, but the burrow doesn't go down into the mining tunnels. The result is that the smelter workshop doesn't see them and they don't show as being available as a job, but assigning them through the manager, ignoring weird workshop stuff, works. It used to happen a lot, less now that hauling stones by hand is a lot slower.
I'm a bit sleepy right now, but basically, if a workshop is in anyway located in the area of a burrow, the materials required for the jobs it offers need to be within that burrow too, or you can't set the work through the workshop. It may not be an issue for all workshops, but known issues arise with smelters and it seems soap makers. It doesn't matter if the burrow is being used by anyone or anything, just its existence causes the problem.