Currently, if a post's comments are locked, you are allowed to try typing a comment in the text field, but then, when you click the Submit button, you get the message "error: Forbidden". I think it would be clearer if the message in this context were changed to "error: Comments are locked".
I was confused by the "error: Forbidden" message just now, because I got it while trying to comment on a post which had initially asked for comments, and was then edited to lock comments while I was in the middle of writing one. Since I was expecting my comment to be allowed, my first thought was that "error: Forbidden" meant that clicking the "submit" button had resulted in a "403 Forbidden" HTTP status code. If that had been the truth, then it would have been reasonable for me to try submitting again after waiting a while and refreshing the page. I didn't realize what was actually going on until I scrolled back up to the post body and noticed that OP had edited it to add "update: problem solved, thanks everyone, locking comments now" to the end.