Несоответствие типа данных в выражении критериев в vb.net с доступом 2010

 Dim QRY As String = "SELECT t1.Observer_Name,t1.Company, t2.Safety, t2.T_Name, t2.Trainer_Name," _
                               + "t2.T_Location, t2.T_Start, t2.T_End,(DateDiff(""d"",T_Start, T_End)+1)*8 as [Man_Hours], t2.Remarks" _
                               + " FROM ObserverDetails t1,Training t2,TrainningAttendee t3" _
                               + " WHERE t2.T_ID=t3.T_ID AND t3.Ob_ID=t1.Observer_ID And  t2.T_Start >= @dt1 AND t2.T_Start <= @dt2 "
        cmdSelect.CommandText = QRY
        cmdSelect.Parameters.Add("@dt1", OleDb.OleDbType.Char).Value = DateTimePicker1.Text.Trim
        cmdSelect.Parameters.Add("@dt2", OleDb.OleDbType.Char).Value = DateTimePicker2.Text.Trim
        cmdSelect.CommandType = CommandType.Text
        cmdSelect.Connection = reportConnection4

        reader1 = cmdSelect.ExecuteReader
        If reader1.Read Then
            While reader1.Read
                Dim row As String() = New String() {" " & reader1.Item("Observer_Name") & " ", "" & reader1.Item("Company") & "", " " & reader1.Item("Safety") & " ", " " & reader1.Item("T_Name") & "", _
                                                   "" & reader1.Item("Trainer_Name") & " ", " " & reader1.Item("T_Location") & "", "" & reader1.Item("T_Start") & "", _
                                                   "" & reader1.Item("T_End") & " ", "" & reader1.Item("Man_Hours") & " ", "" & reader1.Item("Remarks") & " "}
                DataGridView1.Rows.Add(row)
            End While
        End If

выдает ошибку reader = cmdSelect.ExecuteReader. Ошибка несоответствие типа данных в выражении критерия.