SheetChange event

Have you any ideas as to why the sheet change event is not working? I have a before close and before save events and they are fine, it just completely ignores this one. Below is an extract of the code I am using.

--In AppEventClass
Public WithEvents Appl As Application

Private Sub Appl_Workbook_SheetChange(ByVal Sh As
Object, ByVal Source As Range)

Dim ApplicationClass As New AppEventClass ' Creates variable to be used to activate events.

--In Thisworkbook
Private Sub Workbook_Open()
Set ApplicationClass.Appl = Application 'Actives all events created in AppEventClass.
End Sub