JQuery works in Chrome, Firefox, but not IE

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ASP.NET4

Why is it that my JQuery code works well in Chrome and Firefox, but not in IE (version 9). I get a lot of undefined errors when opening my page in IE within the JQuery library code, and my self written code gives the following error: Microsoft runtime error: $ is undefined.

I should also mention that I am making use of a Master page, which references the JQuery as follow:

<script type="text/javascript" src="<%= Page.ResolveUrl("~/Scripts/jquery-1.4.1.min.js")%>"></script>
    <script type="text/javascript" src="<%= Page.ResolveUrl("~/Scripts/blend/jquery.blend.js")%>"></script>
    <script type="text/javascript" src="<%= Page.ResolveUrl("~/Scripts/ui.core.js")%>"></script>
    <script type="text/javascript" src="<%= Page.ResolveUrl("~/Scripts/ui.sortable.js")%>"></script>
    <script type="text/javascript" src="<%= Page.ResolveUrl("~/Scripts/ui.dialog.js")%>"></script>
    <script type="text/javascript" src="<%= Page.ResolveUrl("~/Scripts/ui.datepicker.js")%>"></script>
    <script type="text/javascript" src="<%= Page.ResolveUrl("~/Scripts/effects.js")%>"></script>

And my JQuery as follow:

<script type="text/javascript">
        $(document).ready(function () {
            $('#CloseButton').click(function () {
                $('#myForm').slideUp(1000);
                $('#Screen').css('display', 'none');

                return false;
            });
        });

        function EnlargeSlide() {
            $(document).ready(function () {
                $('#Screen').css({ opacity: 0.7, 'width': $(document).width(), 'height': $(document).height() });
                
                $('#myForm').slideDown('2500');

                return false;
            });
        }

I have similar code in another page, which works well in all browsers.
What might be the issue here?