請問一下...有關於DLL的問題(編號：7865)

請問一下...
假如我有一個用C寫成的manual49.dll,內有一個函式為long myFunc(long num)我用VB6.0呼叫此函式,卻發生錯誤.
請問該如何解決?
Public Declare Function myFunc Lib "c:\258dll\manual49.dll" (ByVal num As Long) As Long
Private Sub Form_Load()
Dim a As Long
　a = myFunc(99)
End Sub