I had accidentally messed up the comments page when I had reuploaded some changes. I forgot to set it to CHMOD 755. Which is why the Internal Server Error 500 was popping up everytime you try to view or add a comment. Sorry about that, it’s fixed now.
In related news, Taylor McKnight has posted some great resources and tips on how to make your Movabletype blog more secure and keep the spammers at bay. If you’re just starting out, or need a refresher, definitely check this post out.