I was having a similar problem, with both crafting as well as upgrading, and aevojoey's solution fixed it for me (thanks!). I went into the save file, searched for any instances of "workers":[] where I knew none of my characters were involved in that activity (there ended up being two instances of this), deleted the hid[ID#] from inside the brackets of the "workers":[], and changed the worker count to 0. When I re-loaded my save everything worked again.