object doesn't support property or method 'mask'

object doesn't support property or method 'mask'

Hi,
I have the following code in my html page. It works if I test it with alert but when I try to run as is I get the error: Microsoft jScript runtime error: Object doesn't support property or method 'mask'

<script src="Scripts/jquery-1.2.8.js" type="text/javascript"></script>
<script src="Scripts/jQuery.maskedinput.js" type="text/javascript"></script>

<script type="text/javascript">
    jQuery(document).ready(function($) {
         $("#txtCommercial").mask("(999) 999-9999");
    });
</script>

Can someone please help me on this?

Thanks Sharon