Thanks for the replies people.

Marto--
You have more than one form on that page, the $mech->field() method defaults to the first form on the page, you need to either specify a form_name or form_number.

This is exactly the error, all I needed to do was specify the form id or number.

Anonymous Monk--
I'm getting this output. I used post because I noticed that it is using the POST method. Error POSTing http://www.attorneycar.com/wp-comments-post.php: Interna +l Server Error at 124.pl line 21

This is happening because Wordpress will make sure to return server errors in case it sees the same post being sent twice (spam control I guess). Try modifying the "comment" field and it should work.