The "quick reply" button is disabled for a reason.
The forum can be used in a linear mode (the default one) and in the threaded mode. In a threaded mode one should know what forum post was the answer to what post. That is why you have to click on the "Quick Reply" button on the particular post.
To
switch to the threaded mode just click "Display mode" link on the top and select "Switch to threaded mode".
You may learn more about using this forum at
http://stream-recorder.com/forum/faq.php
(or click the FAQ link on the top of every page)