I have an ASP.NET 4.0 web form and the Page_Load event fires twice.

I have an ASP.NET 4.0 web form and the Page_Load event fires twice.
I tried setting AutoEventWireup="false" in the page directives and adding Load += new EventHandler(Page_Load); in code behind,  but it still fires twice.
I read that image tags missing alt or src attributes may be the cause but these are my three image tags and they all render fine:
 <asp:Image ID="ImageCollapsible" runat="server" AlternateText="Collapsible" ImageUrl="~/Images/collapse.jpg"  /> <img alt="progress..." src="images/progress.gif"/> <img src="Images/Schrodinger_Logo.gif" alt="Logo" /> From what I have read a suspect the culprit may be a tag in the ASP page missing an attribute and that it could cause the browser to try to load the page twice looking trying to retrieve missing information.
If anybody readin ...