I have the following subroutine

VBAProject (PERSONAL.xlsb)

Modules

Module1

Sub Auto_Open()

Dim Shortcut As CommandBar
Dim NewItem As CommandBarButton
Set Shortcut = Application.CommandBars("Cell")
Set NewItem = Shortcut.Controls.Add()
With NewItem

Caption = "Insert C Comment"
OnAction = "AddComment"

End With
MsgBox ("Test")

End Sub

which should add a new item to the right click/context menu titled "Insert C Comment", which when clicked, calls the subroutine AddComment() (also stored in Module1).

If I run the routine with Excel already open, everything works as expected. However, if I initially open Excel, my understanding is that a subroutine named Auto_Open stored as above should run automatically. And indeed it does, as evidenced by the test MsgBox being displayed. However recently even though the subroutine runs, "Insert C Comment" is *not* added to the context menu. Some time ago it was inserted ok, and later it was inserted twice(!), but now it's not inserted at all. Any ideas as to what's going on?