Issue with jQuery: Background-Position Animation Plugin - error in IE8

Issue with jQuery: Background-Position Animation Plugin - error in IE8

Hi
When I attempt to use this plugin I get the infamous IE error "null or not an object" - full details follow...

-------------------------------
Webpage error details

User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 3.5.30729; .NET CLR 3.0.30729; OfficeLiveConnector.1.5; OfficeLivePatch.1.3; .NET CLR 1.1.4322; .NET4.0C; Tablet PC 2.0; .NET4.0E)
Timestamp: Sat, 27 Nov 2010 12:38:34 UTC


Message: '1' is null or not an object
Line: 42
Char: 3
Code: 0
URI: file:///C:/Users/Test/Documents/Sites/test.fr/trunk/public_html/wpscripts/ jquery.backgroundPosition.js

I am using v1.21 of the "trixta" developed jQuery: Background-Position Animation Plugin and I am calling it as follows...

<script type="text/javascript">
<!--
//move the background
moveBgAround();

function moveBgAround() {
// give a random value from 0 to 2000 for the X axis set Y axis to 0
var x = Math.floor(Math.random()*2000);
var y = 0;

// make the background image move!
$('.scrollBg').animate({backgroundPosition: (x * -1) + 'px ' + '0px'}, 2500, "swing", function() {moveBgAround();});

};
-->
</script>

I have placed this within a "document ready" call in the header and also inline with the body HTML... both fail with the same error, same place.  Have been stuck on this one for a while - especially as it is a plugin I have used before with a similar calling method (I was randomizing x, y and time in that one - this is a simplified call)... and that works in IE8 (the site is www.bymia.fr).

So... any ideas as to why this is failing? As usual for this error, I get this script instance to work in other browsers (including Opera, Safari [Mac & Windows], Chrome, Firefox)...

Thanks in advance...

Andrew