OnselectedIndexChanged causing a NullReferenceException

[samflex]

Greetings. This is not making a whole lot of sense to me. I have a dropdownList that is dynamically populated from the database. This works. However, I have an OnselectedIndexChanged event tied to this DropDownList that when a user selects an item from the DropDownList, an associated value is stored on a textbox. This was working when used a regular webform. However, due to the complicated nature of some other controls, I had to switch to Repeater control. Now, this

OnselectedIndexChanged event

is not working any longer. When I select a value from the DropDownList, it throws the following error: System.NullReferenceException: Object reference not set to an instance of an object, pointing to the SQL select statement line. What am I missing please?

                         $
                     

Protected Sub ddlWater\_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
    Using con As SqlConnection = New SqlConnection(constring)
        Dim txt\_amount As TextBox = CType(DynamicRepeater.FindControl("txt\_amount"), TextBox)
        Dim dt As New DataTable()
        Dim ddlWater As DropDownList = CType(DynamicRepeater.FindControl("ddlWater"), DropDownList)
        con.Open()
        Dim sql As String = " SELECT RebateAmount FROM WaterVolume WHERE WaterSizes = '" & ddlWater.SelectedValue & "' "
        Response.Write(sql)
        Response.End()
        Dim cmd As SqlCommand = New SqlCommand(sql, con)
        Dim ad As SqlDataAdapter = New SqlDataAdapter(cmd)
        ad.Fill(dt)

        If dt.Rows.Count > 0 Then
            txt\_amount.Text = dt.Rows(0)("Amount").ToString()
        End If
    End Using
End Sub

Error is on this line below:

Dim sql As String = " SELECT RebateAmount FROM WaterVolume WHERE WaterSizes = '" &

Thank you in advance