Ah, that's what I'm testing with. Sorry, I could replicate your problem by deliberately passing a "null" (read: nonexistent) skill into drawNonDualSkillCost, confirming my original hunch about what's happening... but I have no clue as to why it's getting a bad skill from where I'm sitting. Is this the only dualtech your actor has learned? And are you sure every other skill they have learned is valid? (Like, and I'm just making a suggestion here, you didn't teach the actor skill #189 and then reduced the skill list to 170 or something like that?) EDIT: No, if it's going to DrawComponentSkillCost, that last one doesn't seem likely.