cannot update wpf datagridview cell data using linq to sql

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C#

WPF

LINQ

private void btnUpdate_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                comocoLTSDataContext dc = new comocoLTSDataContext();
                DCdate dateRow = dataGrid1.SelectedValue as DCdate;
                //int m = dateRow.GKId;
                DCdate date = (from d in dc.DCdates
                               where d.GKId == dateRow.GKId & d.DId==dateRow.DId & d.DCcontainer.ContainerNo==txtContNo.Text
                               select d).Single();
                date.Date1 = dateRow.Date1;
                date.Temp00 = dateRow.Temp00;
                date.Temp06 = dateRow.Temp06;
                date.Temp12 = dateRow.Temp12;
                date.Temp18 = dateRow.Temp18;
                date.DLane = dateRow.DLane;
                date.DVentilation = dateRow.DVentilation;
                date.DRemarks = dateRow.DRemarks;
                dc.SubmitChanges();
                MessageBox.Show("Row Updated Successfully");
                LoadDates();


            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
                return;
            } 

        }

this is how I tried to update my db using datagridview. code seems to be ok. also giving the "Row updated" message. but when call LoadDates() Db has not been updated.

please help me soon...

why can't anyone give me a reason.....