C is the confirm button, right?
So what? You're using the skill?
Not like I'm a professional scripter or expert by any means, but knowing what I know about the system, and judging by the error, I'd wager maybe you have no cast time specified for the skill used?
Seeing the error is one thing, but like Zer0 said above, it'd be best to upload a copy of your project so that someone can test it themselves and see if they can solve the issue.
--J