Javascript popup error with long messages

[netarus]

Whenever I post a very long message, the following window appears every couple of seconds:

XMLHttpRequest Open Failed!
This can happen if the URL you are accessing the product from (http://www.domain.com/support) is different than the one specified under Admin CP > Settings > General (Ex: http://support.domain.com/). Due to limitations of AJAX, The URL should be *exactly* the same as specified under Product URL setting.

This only seems to show after a certain number of characters are entered into the 'Contents' field with a 'Post Reply' within the Staff portal.

I have triple checked these settings and the URL that I am at matches the settings in the admin panel. Any thoughts?