Post the solution.
I suggest disabling locking in the help forums. I'd estimate well over 90% of the use it gets here is not because the topic is better off if no further posts are made, which is the only case where it should be used. I would speculate that people only use it because they have it - "Because this thread is mine, I have the authority to close it. The prospect of having authority of any sort excites me, so I will lock the topic." In any case, it would not be missed if removed. Perhaps it could even be replaced by a fake lock button that redirects them to a page reminding them to post the solution if they haven't already.