Larry,
Check your quick reply box template (showthread_replybox if you're using Firefly's hack) and make sure the name of your quick reply form is "vbform".
It should look like this:
Code:
<form enctype="multipart/form-data" action="newreply.php" name="vbform" method="post" onSubmit="return validate(this)">
Then scroll down a little and make sure your textarea name is "message".. It should look like this:
Code:
<textarea name="message" rows="7" cols="$textareacols" wrap="virtual" tabindex="1"></textarea>
Thats about the only thing that could cause a javascript error.