"Specified cast is not valid" Message in Outlook Automation Application.

I want my application to catch ItemRemove, ItemChange and ItemAdd events. So I created my class (see below).
BUT! My application crashes with "Specified cast is not valid" error. When I use familiar code in VBA (In Microsoft Office XP environment) everything is ok!

Anyone get help me out?

Public Class Exchange
Private m_OutlookApp As Outlook.ApplicationClass
Private m_NameSpace As Outlook.NameSpace
Private WithEvents m_Items As Outlook.Items

Public Sub UnInitialize()
m_NameSpace.Logoff()
m_OutlookApp.Quit()
End Sub

Public Sub Initialize()
m_OutlookApp = New Outlook.ApplicationClass()
m_NameSpace = m_OutlookApp.GetNamespace("MAPI")
m_NameSpace.Logon("", "", False, True)
m_Items = m_NameSpace.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderContacts)
End Sub

Private Sub m_Items_ItemAdd(ByVal Item As Object) Handles m_Items.ItemAdd
Dim myItem As Outlook.ContactItem
MsgBox(myItem.FullName)
End Sub

Private Sub m_Items_ItemChange(ByVal Item As Object) Handles m_Items.ItemChange
Dim myItem As Outlook.ContactItem
MsgBox(myItem.FullName)
End Sub

Private Sub m_Items_ItemRemove() Handles m_Items.ItemRemove
End Sub
End Class