No preview image?

Hi,

I just found JW Player and added it on a test site of mine - it works but there is no preview image, just the "black screen" with the play-button in it:

http://www.ki.tng.de/~petermarwitz/in7days/referenzen-videos.html

And this is the code (copying the one from the instruction screen):
<script type='text/javascript' src='player/swfobject.js'></script>
<script type='text/javascript'>
var s1 = new SWFObject('player/player.swf','player','400','300','9');
s1.addParam('allowfullscreen','true');
s1.addParam('allowscriptaccess','always');
s1.addParam('flashvars','file=fuehrerschein-mit-17-sat1.flv');
s1.addParam('image','http://www.peter-marwitz.de/in7days/player/fuehrerscheinmit17.jpg');
s1.write('preview');
</script>

What am I missing? Thanks!