System.InvalidCastException: Specified cast is not valid

Försöker fylla en datalist med den här koden

Dim objconn As New OleDbConnection(ConfigurationSettings.AppSettings("connectionstring"))
    Public dl_poll As DataList
    Public error6 As Label
    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If Not (IsPostBack) Then
            bindgrid()
        End If
    End Sub

    Private grupp As String = ""
    Public Property _pid() As String
        Get
            grupp = grupp
        End Get
        Set(ByVal Value As String)
            grupp = Value
        End Set
    End Property

    Public Sub bindgrid()

        Dim objcmd As New OleDbDataAdapter _
            ("select [id],[votes],[pid],[alternativ] from [votes] where [pid]=" & grupp & " order by [id] desc", objconn)

        Dim ds1 As DataSet = New DataSet()
        objcmd.Fill(ds1, "poll1")

        dl_poll.DataSource = ds1.Tables("poll1"). _
        DefaultView
        DataBind()
    End Sub

Får det här felmeddelandet

Source Error: 

Line 49:         dl_poll.DataSource = ds1.Tables("poll1"). _
Line 50:         DefaultView
Line 51:         DataBind()
Line 52:     End Sub
Line 53: 
 

Source File: h:\inetpub\wwwroot\tibroik.net\poll.ascx.vb    Line: 51

Någon som vet vad som kan vara fel?

dl_poll.databind()

har redan provat det och det ger samma fel

Detta funkar alltså inte?

dl_poll.DataSource = ds1.Tables("poll1").DefaultView
dl_poll.DataBind()

nej.