can’t change directory for comments

I know what the problem is, but I’m not sure how to fix it.
My blog is in a subdirectory, i.e. http://www.mywebsite.com/blog

Which has worked fine for everything but comments. When I, or anyone tries to submit a comment, as soon as they select the submit button, an error page appears which says, “The requested URL /wp-comments-post.php was not found on this server.” It tries to load the comments here:
http://www.mywebsite.com/wp-comments-post.php

I’ve updated the blog URI in Options/General to reflect the proper directory, but comments just seem to want to go home. What am I missing here?