ExtJS 4 and ASP.Net - renderTo on MasterPage

Hello,

I have a problem with the renderTo property while using it with asp.net master pages, and my ext js code is on a separated file. The problem is that the panel do not render.

Extjs.js

Code:

var myPanel = Ext.create('Ext.TabPanel', {
    renderTo: 'myDivId',
    ...
});

home.aspx

Code:

<asp:Content ID="Content2" ContentPlaceHolderID="cphHeader" runat="server">
        <script type="text/javascript" src="Extjs.js"></script>
</asp:Content>


<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
        <div id="myDivId">
        </div>
</asp:Content>

If i use like this, don't work but if put my all the javascript code inside the script tag on the aspx file, works just fine.

Code:

<script type="text/javascript">
var myPanel = Ext.create('Ext.TabPanel', {
    renderTo: 'myDivId',
    ...
});
</script>

Someone knows this problem ? renderTo is not finding my DIV by the ID if the code is not on the same file, how can I resolve this ?

thanks

ExtJS 4 and ASP.Net - renderTo on MasterPage