You may also want to clear your cache. This process is different for each browser, so go to Help at the top of your browser window, and search "clearing the cache".
Let us know if that works.
Emily
This sounds like a glitch to me. We don't have a way to prevent people from commenting on a user's post that still enables them to start their own. What happens when you try to post on an existing thread? If you need to start a new thread to answer, feel free. It might be easier, though, to use the "Contact Us" link at the bottom of any page to send us an email message so we can correspond and figure out the problem. So sorry this is happening to you!