Set Custom error page for all Application label error and error code also

//  IN Global.asax Under Application_Error

void Application_Error(object sender, EventArgs e)

    {

        //////////// Code that runs when an unhandled error occurs

        //Response.Redirect("~/Error Page Not Found");

        Exception ex = Server.GetLastError();

        Application["TheException"] = ex; //store the error for later

        Server.ClearError(); //clear the error so we can continue onwards

        Response.Redirect("~/Error Page Not Found"); //direct user to error page

    }

// IN web.config file Under

  <system.web>

<!--<customErrors mode="Off"></customErrors>-->

<customErrors mode="RemoteOnly" defaultRedirect="~/Error Page Not Found"></customErrors>

  </system.web>

<system.webServer>

    <httpErrors errorMode="Custom" defaultResponseMode="Redirect">

      <remove statusCode="404" subStatusCode="-1" />

      <error statusCode="404" prefixLanguageFilePath="" path="~/Error Page Not Found"

       responseMode="Redirect" />

    </httpErrors>

    <validation validateIntegratedModeConfiguration="false"/>

</system.webServer>