I was on here a few weeks ago with a broken comment problem. It was taking my users to a 500 Internal Error page.
I did what the other user suggested and it worked like a charm. Now - again without changing anything that I know of - commenters can access the comments page and attempt to leave a comment, which looks like it's going to post and instead takes you to a page that never loads. I've tried myself, logged in, and have had the same problem.
It's standsalone.org/blog. I'd appreciate it if someone could check it out. Comments worked until at least Jan 18th. I swear I haven't modified anything since.