I have a datalist that bind several dropdownlists from various tables. Well two of the dropdownlist are dependent upon the other. For example, if ddl1.SelectedValue = "1" then ddl2.selectedvalue = '01'. If ddl1.SelectedValue ="2" then ddl2.selectedvalue = '02'. If it was outside of a datalist then I would have no problem doing it. But instead this datalist is really throwing me off. Any suggestions. I'm not sure whether or not to use ItemDataBound or dlSelectedIndexChange. Here my code that I have thus far. Right now it's throwing the error "Object reference not specified" on the line
 'prmCauseDetail.Value = ddlcausetype.SelectedItem.Value'

Private Sub BindCauseDetails(ByVal ddl As DropDownList)

        connFF = New SqlConnection(Application("connFF"))
        Dim ddlcausetype As DropDownList
        Dim intCounter As Integer
        Dim ddlCauseDetails As DropDownList
        Dim cmdCauseDetails As New SqlCommand("spFFGetCauseDetails", connFF)
        cmdCauseDetails.CommandType = CommandType.StoredProcedure

        Dim prmCauseDetail As New SqlParameter("@CauseType", SqlDbType.VarChar)
        prmCauseDetail.Value = ddlcausetype.SelectedItem.Value
        cmdCauseDetails.Parameters.Add(prmCauseDetail)

        Dim dtrDetails As SqlDataReader

        Try
            connFF.Open()
            dtrDetails = cmdCauseDetails.ExecuteReader
            ddlCauseDetails.DataSource = dtrDetails
            ddlCauseDetails.DataTextField = "Details"
            ddlCauseDetails.DataValueField = "Details"
            ddlCauseDetails.DataBind()

            dtrDetails.Close()
            connFF.Close()

        Catch er As Exception
            LogError(er.ToString, "CauseDetails-Incident.aspx")
            Exit Try
        Finally
            connFF.Close()
        End Try
    End Sub

    Sub dlIncident_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles dlIncident.SelectedIndexChanged
        Dim ddlCausedetails As DropDownList
        BindCauseDetails(ddlCausedetails)
    End Sub

<asp:DropDownList id="ddlcausetype" runat="server" OnSelectedIndexChanged="dlIncident_SelectedIndexCh anged"
                                        Width="272px" ForeColor="Gray" AutoPostBack="True"></asp:DropDownList></TD>