請問 ReplaceText API 該如何測試(編號:4619)

請問 ReplaceText API 該如何測試,我以下列程式測試總會出現現'這個程式執行作業無效,即將關閉' 的錯誤訊息',
PS:表單內只有一個Text1及兩個Command Button
使用Win98se + vb6 + sp3 程式碼如下:

Option Explicit
'Find/Replace Type Structure
Private Type FINDREPLACE
lStructSize As Long
 hwndOwner As Long
 hInstance As Long
 flags As Long
 lpstrFindWhat As String
 lpstrReplaceWith As String
 wFindWhatLen As Integer
 wReplaceWithLen As Integer
 lCustData As Long
 lpfnHook As Long
 lpTemplateName As String

End Type

'Common Dialog DLL Calls
Private Declare Function FindText Lib "comdlg32.dll" _
Alias "FindTextA" (pFindreplace As FINDREPLACE) As Long

Private Declare Function ReplaceText Lib "comdlg32.dll" _
Alias "ReplaceTextA" (pFindreplace As FINDREPLACE) As Long

'Delcaration of the type structure
Dim frText As FINDREPLACE

Private Sub cmdFind_Click()
'Call the find text function
frText.lpstrFindWhat = Text1.SelText
FindText frText

End Sub

Private Sub cmdReplace_Click()
'Call the replace text function
ReplaceText frText
End Sub

Private Sub Form_Load()
'Set the Find/Replace Type properties
With frText
.lpstrReplaceWith = "Replace Text"
 .lpstrFindWhat = "Find Text"
 .wFindWhatLen = 9
 .wReplaceWithLen = 12
 .hInstance = App.hInstance
 .hwndOwner = Me.hWnd
 .lStructSize = LenB(frText)

End With
End Sub