Sorry for the delay, was at work
Not really sure why it isn't working for some, only thing I can think of is a conflict somewhere. Try removing this from the block_countdown template and add it to your headinclude or footer (footer is my own preference)
Code:
<script language="Javascript" type="text/javascript" src="countdown/js/jquery-1.4.1.js"></script>
<script language="Javascript" type="text/javascript" src="countdown/js/jquery.lwtCountdown-1.0.js"></script>
<script language="Javascript" type="text/javascript" src="countdown/js/misc.js"></script>
<link rel="Stylesheet" type="text/css" href="countdown/style/main.css"></link>
If anyone wants to PM me a link to their site I'll have a look, it is hard to try find a solution because it has worked on every site I've installed it on