301 redirect problem

I am trying to set up 301 redirect so that www.site.com, www.site.com/index.aspx, site.com all point to the same page.

To do that I am using following setting in web.config file:

str=http://www.nexthermal.in/index.aspx
currentUrl=/index.aspx

 <%-- string url = HttpContext.Current.Request.Url.AbsoluteUri;
        Response.Write("str=" + url );
        Response.Write("currentUrl=" + currentUrl );
        Response.End();--%>
url=/Index.aspx

However, I get the following error:

  [System.Diagnostics.DebuggerNonUserCodeAttribute()]
   public global_asax() {
  if ((global::ASP.global_asax.@__initialized == false)) {