There is no row at Position 1

dim nums as String = Request("marks")

           If Not Int32.TryParse(nums, num) Then

               For i = 0 To num
                   cmd.CommandText = "select * from test where Serial=" & a(i)
                   adp = New SqlDataAdapter(cmd.CommandText, cnn)
                   adp.Fill(ds, "test")
               Next

           End If







           cnn.Close() 'connection closed


           'this code is for creating new a table "preferably ANSWERED TABLE"
           dt = New DataTable("Answered")
           dt.Columns.Add("Serial", GetType(Integer))
           dt.Columns.Add("question", GetType(String))
           dt.Columns.Add("choice1", GetType(String))
           dt.Columns.Add("choice2", GetType(String))
           dt.Columns.Add("choice3", GetType(String))
           dt.Columns.Add("choice4", GetType(String))
           dt.Columns.Add("correct", GetType(String))
           dt.Columns.Add("selected", GetType(Integer))


           'this code is for adding to the table TEST
           Dim r As DataRow

           For Each r In ds.Tables("test").Rows
               dr = dt.NewRow
               dr("Serial") = dt.Rows.Count + 1
               dr("question") = r.Item("question")
               dr("choice1") = r.Item("choice1")
               dr("choice2") = r.Item("choice2")
               dr("choice3") = r.Item("choice3")
               dr("choice4") = r.Item("choice4")
               dr("correct") = r.Item("correct")
               dr("selected") = -1
               dt.Rows.Add(dr)

           Next

           Session("Answered") = dt

           Call show()

           If ctr = 0 Then
               BtnPrev.Enabled = False


           End If


       End If
   End Sub
   Sub show()
       dt = Session("Answered")
       Dim v As View = Me.View1


       Dim l As Label
       l = CType(v.FindControl("Label1"), Label)
       l.Text = dt.Rows(ctr).Item("Serial") & "."
       l = CType(v.FindControl("Label2"), Label)
       l.Text = dt.Rows(ctr).Item("question")



       Dim r As RadioButtonList
       r = CType(v.FindControl("RadioButtonList1"), RadioButtonList)
       r.Items.Clear()
       r.Items.Add(dt.Rows(ctr).Item("choice1"))
       r.Items.Add(dt.Rows(ctr).Item("choice2"))
       r.Items.Add(dt.Rows(ctr).Item("choice3"))
       r.Items.Add(dt.Rows(ctr).Item("choice4"))
       r.SelectedIndex = dt.Rows(ctr).Item("selected")



       Session("ctr") = ctr
   End Sub