[jQuery] error when using a timeout

[matthewordie]

I'm using this plugin to animate some background images:
http://plugins.jquery.com/project/backgroundPosition-Effect

Now it works fine until I wrap the animate function in a timer. Then
it gives me errors. I'm changing the image on hover. Here's my code:

var hideDelay = 2000;
var hideDelayTimer = null;

                $(".tab_item").mouseover(function() {
                        if (hideDelayTimer) clearTimeout(hideDelayTimer);
                        $(this).animate({
                                backgroundPosition: '(0 100px)'
                        });

                }).mouseout(function(){
                        if (hideDelayTimer) clearTimeout(hideDelayTimer);
                        hideDelayTimer = setTimeout(function () {
                               $(this).animate({backgroundPosition: '(0 0)'});
                                hideDelayTimer = null;
                        }, hideDelay);

                });


Any ideas why it wouldn't fire like this? Here's the error message:
uncaught exception: [Exception... "Could not convert JavaScript
argument arg 0" nsresult: "0x80570009 (NS_ERROR_XPC_BAD_CONVERT_JS)"
location: "JS frame :: 
http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js
:: anonymous :: line 12" data: no]