Cannot comment on localhost

I have just started learning the ins and outs of WordPress and am developing a site under XAMPP on my local machine for educational purposes.

I am at the point in development where I have added the comments_popup_link() function into my index. However, when I click on the generated link, instead of displaying comments, or taking me to the new comment form, I instead receive this error:
[an error occurred while processing this directive] You don't have permission to access the requested object. It is either read-protected or not readable by the server. [an error occurred while processing this directive]

I get the same error if I use the supplied 2010 theme, as well. I am able to post posts through the control panel, and edit_post_link() functions correctly.

What are probable causes of this?

Thanks.