枚举和输出outlook sent items文件夹中的项目的问题

Question

正如标题所说，我在Outlook中的已发送项目文件夹中枚举和输出项目时遇到问题。具体来说，我正在寻找已发送的任务。它一直告诉我文件夹中没有任何内容。代码是：

   Private Sub GetSentTasks(objApp As Microsoft.Office.Interop.Outlook.Application)
        Dim objNS As Outlook.NameSpace = objApp.GetNamespace("MAPI")
        Dim folder As Outlook.MAPIFolder = _
            objNS.GetDefaultFolder( _
            Outlook.OlDefaultFolders.olFolderSentMail)

        Dim searchCriteria As String = "[MessageClass] = 'IPM.TaskRequest'"
        Dim strBuilder As StringBuilder = Nothing
        Dim counter As Integer = 0
        Dim taskItem As Outlook._TaskItem = Nothing
        Dim folderItems As Outlook.Items = Nothing
        Dim resultItem As Object = Nothing
        Dim TTDcounter As Integer = 0
        Try
            folderItems = folder.Items
            folderItems.IncludeRecurrences = True
            If (folderItems.Count > 0) Then
                resultItem = folderItems.Find(searchCriteria)
                If Not IsNothing(resultItem) Then
                    strBuilder = New StringBuilder()
                    Do
                        If (TypeOf (resultItem) Is Outlook._TaskRequestItem) Then
                            counter += 1
                            taskItem = resultItem



                            'If taskItem.Categories = "TTD" Then
                            TTDcounter += 1
                            Dim listarray() As String = {taskItem.Delegator, taskItem.Subject, taskItem.DueDate, stripEstComp(taskItem.Body.ToString())}
                            taskPaneControl3.ListView1.Items.Add(TTDcounter).SubItems.AddRange(listarray)
                            'End If


                        End If
                Marshal.ReleaseComObject(resultItem)
                resultItem = folderItems.FindNext()
                    Loop Until IsNothing(resultItem)
                End If
            End If
            If Not IsNothing(strBuilder) Then
                Debug.WriteLine(strBuilder.ToString())
            Else
                Debug.WriteLine("There is no match in the " + _
                                   folder.Name + " folder.")
            End If
        Catch ex As Exception
            System.Windows.Forms.MessageBox.Show(ex.Message)
        Finally
            If Not IsNothing(folderItems) Then Marshal.ReleaseComObject(folderItems)
        End Try
    End Sub