C# Entity Framework The ObjectContext instance has been disposed and can no longer be used for operations that require a connection

The ObjectContext instance has been disposed and can no longer be used for operations that require a connection

        public override void Dispose()
        {
            string objectContextKey = "MIP_" + HttpContext.Current.GetHashCode().ToString("x"); if (HttpContext.Current.Items.Contains(objectContextKey))
            {
                SPMIPEntities ctx = HttpContext.Current.Items[objectContextKey] as SPMIPEntities; if (ctx != null)
                {
                    ctx.Dispose(); HttpContext.Current.Items.Remove(objectContextKey);
                }

            }
            base.Dispose();
        }