[jQuery] does ie (6 / 7) have problems with animate ?

[jQuery] does ie (6 / 7) have problems with animate ?


$styleDir = "http://someurl";
$j('#MainNavi ul').css({'background':'url(' + $styleDir +
'/img/MainNavi/MainNavi_bg.png) repeat-x !important'});
IE6/7 throws a js-error: 'illegal argument'.
What can that be ?
micha