Error on retrieving data for a web grid

What is the usual cause of failure and then getting this message.  The code that is feeding the webrid is below the error message  - trying to figure where to look.

Thanks DonnieS

HTTP Error 500.21 - Internal Server Error

Handler "PageHandlerFactory-Integrated" has a bad module "ManagedPipelineHandler" in its module list

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Xml;
using TOBI.Data;
using TOBI.Data.Models;
using EnityRepository;


namespace TOBIE.BA.BankChecks
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        private TOBIE_BAContext db = new TOBIE_BAContext();

        protected void Page_Load(object sender, EventArgs e)
        {
            var bankchecks = new EFRepository<bankchecks_CashBook>(db);
            GridView1.DataSource = bankchecks.GetAll();
            GridView1.DataBind();
        }
    }
}