There is this error message:
The comment could not be accepted because it got flagged as SPAM by our anti-SPAM measures (ERR: 01).
What indicates that you are using the TOKEN from the spam control options.
But I cannot find the necessary <TOKEN> tag in your add comment or reply comment form (why do you have it twice?)
You use something I never saw, this one:
<input id="you_are" type="hidden" value="aspambot" name="you_are"/>
So please check your token settings, although I cannot imagine why it is working fine on a new comment and not on reply comments. Most probably it has something to do with the order in which the Addons are called which use the same workspace
I guess, you don't use Defensio, do you? Reply-To-Comments Addon doesn't work together with Defensio, only with Akismet