Dim sPath As String = "LDAP://mydomain.de"
            Dim myDirectory As New DirectoryEntry(sPath, "admin", "123456")            
            Dim mySearcher As New DirectorySearcher(myDirectory)
            Dim mySearchResultColl As SearchResultCollection
            Dim mySearchResult As SearchResult
            Dim myResultPropColl As ResultPropertyCollection
            Dim myResultPropValueColl As ResultPropertyValueCollection
            mySearcher.Filter = ("(objectClass=user)")
            mySearchResultColl = mySearcher.FindAll()
            Dim result As SearchResult
 
            ' Loop all
            For Each result In mySearchResultColl
                Dim User As New System.DirectoryServices.DirectoryEntry( _
                  result.Path)
                ListBox1.Items.Add(User.Properties("mail").Item(0)) ' Diese 
                ' Zeile verursacht den Fehler
                User = Nothing
            Next result