System.NullReferenceException: Riferimento a un oggetto non impostato su un'istanza d

[mexican]

Ragazzi cosa vuol dire???
Mi da l'errore dove ho messo una label.visible=true ed una false.
ma che sbaglio?

If stipo = "contraente" Then
contraente.Visible = True
proprietario.Visible = False
Else
contraente.Visible = False
proprietario.Visible = True
End If

[sms]

codice completo della pagina? grazie
forse manca un New da qualche parte

[mexican]

mports System.Data.OleDb
Imports System.Configuration.ConfigurationSettings


Public Class WebForm5
Inherits System.Web.UI.Page

Protected conn As OleDbConnection
Protected cmdSql As OleDbCommand
Protected strsql As String = ""
Protected rs As OleDbDataReader
Public snome As String, scognome As String, spiva As String, stipo As String
Protected WithEvents lista As System.Web.UI.WebControls.Repeater
Protected WithEvents nome As System.Web.UI.WebControls.TextBox
Protected WithEvents cognome As System.Web.UI.WebControls.TextBox
Protected WithEvents piva As System.Web.UI.WebControls.TextBox
Protected WithEvents tipo As System.Web.UI.WebControls.DropDownList
Protected WithEvents contraente As System.Web.UI.WebControls.Label
Protected WithEvents proprietario As System.Web.UI.WebControls.Label




Sub connetti()
Dim strconn As String
strconn = "Provider=Microsoft.Jet.OleDb.4.0; Data Source=" & Server.MapPath(".") & "\" & ConfigurationSettings.AppSettings("nomeDB")
conn = New OleDbConnection(strconn)
conn.Open()
End Sub

#Region " Codice generato da Progettazione Web Form "

'Chiamata richiesta da Progettazione Web Form.
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

End Sub

Protected WithEvents messaggio As System.Web.UI.WebControls.Label
Protected WithEvents cerca As System.Web.UI.WebControls.Button

'NOTA: la seguente dichiarazione è richiesta da Progettazione Web Form.
'Non spostarla o rimuoverla.
Private designerPlaceholderDeclaration As System.Object

Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
'CODEGEN: questa chiamata al metodo è richiesta da Progettazione Web Form.
'Non modificarla nell'editor del codice.
InitializeComponent()
End Sub

#End Region

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'Inserire qui il codice utente necessario per inizializzare la pagina
If Request.QueryString("provenienza") = "dettaglio" Then
connetti()
'Try
contraente.Visible = False
proprietario.Visible = False
BindLista(Request.QueryString("nome"), Request.QueryString("cognome"), Request.QueryString("piva"), Request.QueryString("tipo"))
'Catch ex As Exception
'messaggio.Text = "Errore: " & ex.Message()
'Finally
conn.Close()
'End Try
End If
End Sub

Private Sub cerca_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cerca.Click

'Try
snome = nome.Text
scognome = cognome.Text
spiva = piva.Text
stipo = tipo.SelectedItem.Value
BindLista(snome, scognome, spiva, stipo)

'Catch ex As Exception
'messaggio.Text = "Errore: " & ex.Message()

'End Try
End Sub
Public Sub BindLista(ByVal snome As String, ByVal scognome As String, ByVal spiva As String, ByVal stipo As String)
connetti()
'Try
strsql = "Select * from CLIENTI where"

If stipo = "contraente" Then
If snome <> "" Then
strsql = strsql & " nome_c like '%" & Replace(snome, "'", "''") & "%' and"
End If
If scognome <> "" Then
strsql = strsql & " cognome_c like '%" & Replace(scognome, "'", "''") & "%' and"
End If
If spiva <> "" Then
strsql = strsql & " piva_c='" & Replace(spiva, "'", "''") & "' and"
End If

If Right(strsql, 5) = "where" Then
strsql = Mid(strsql, 1, Len(strsql) - 5)
End If
If Right(strsql, 3) = "and" Then
strsql = Mid(strsql, 1, Len(strsql) - 3)
End If


cmdSql = New OleDbCommand(strsql, conn)
rs = cmdSql.ExecuteReader()
lista.DataSource = rs
lista.DataBind()
rs.Close()

Else
If snome <> "" Then
strsql = strsql & " nome_p like '%" & Replace(snome, "'", "''") & "%' and"
End If
If scognome <> "" Then
strsql = strsql & " cognome_p like '%" & Replace(scognome, "'", "''") & "%' and"
End If
If spiva <> "" Then
strsql = strsql & " piva_p='" & Replace(spiva, "'", "''") & "' and"
End If

If Right(strsql, 5) = "where" Then
strsql = Mid(strsql, 1, Len(strsql) - 5)
End If
If Right(strsql, 3) = "and" Then
strsql = Mid(strsql, 1, Len(strsql) - 3)
End If


cmdSql = New OleDbCommand(strsql, conn)
rs = cmdSql.ExecuteReader()
lista.DataSource = rs
lista.DataBind()
rs.Close()
End If

If stipo = "contraente" Then
contraente.Visible = True
'proprietario.Visible = False
Else
'contraente.Visible = False
proprietario.Visible = True
End If

'Catch ex As Exception
'messaggio.Text = "Errore: " & ex.Message()
'Finally
conn.Close()
'End Try
End Sub

End Class