Web Forms :: Display Complete Exception Details And Error Message On Custom Error Page

I am trying to handle the unhandled exceptions in my project.I tried with this following code in my web.config filebut it is not at all redirecting to an error page which i have created instead of that it is throwing an exception in my code itselef. How to print the error description over therein my custom error page.

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<sys.web>......<customErrors mode="On" defaultRedirect="~/Error.aspx"></customErrors>...</sys.web>
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And even i tried in Global.asax page in Application_Error() method like below

 Exception ex = Server.GetLastError();Response.Redirect("~/Error.aspx?errmsg="+ex.message);Server.ClearError();

And in my Error.aspx.cs page i have placed a label and i have written code like this

protected void Page_Load(object sender, EventArgs e)         {
         Label1.Text=Request["errmsg"];
      }

But it is not getting redirected my error page and not displaying anything on it.