I just inherited a web site that was created by a designer. The site was originally created with all *.html files. The designer renamed all the *.html files to *.aspx files.
Based on what I found here: http://forums.asp.net/t/1229894.aspx/1
In your aspx in page attribute add
AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="Default"
Similarly in your class file that you just added remove everything. Your class should look like this:
//all namespaces go here
public partial class Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
}