Submitting comments in the Discussion tab results in 404 Error

I recently set up a wiki on my blog using the wiki plug-in.
I want the wiki to operate in a way that anyone (without signing into the blog etc) can modify the contents of the wiki, including the comments.
But whenever someone posts a comment on the discussion tab, or tries to sign up for the RSS feed, it gives you the following error. Does anyone know how to fix this problem?

Error 404 - Not Found
Ooops, I cannot find you the page you are looking for. You may try to search my site another keyword or use the navigation on your right to browse my site.

The wiki can be found here: