Please upgrade to 2.2 here.
The 2.0 and 2.1 branches are no longer being updated.
[ReplyTo addon] ReplyTo Prevents Ajaxed Comments
This discussion is related to the ReplyTo
The ReplyTo plugin is preventing comments from being submitted without a page reload. I ran several tests on a fresh install to confirm. The problem affects replies as well as normal comments. Any idea how to fix this?