Run Mouse Right Click Macro From Add-In

Hi
I have a large project that I've been able to move all code from the workbook to an Add-In (except code that's sheet related). I have one module that refuses to run from the Add-In. In this code

Public Sub Auto_Open()
With Application.CommandBars("Cell").Controls
        With .Add(temporary:=True)
            .Caption = "Calculate"
            .OnAction = "Calculate"
        End With
    End With
End Sub

a "Calculate" command is added to the mouse right click menu. The command is supposed to call this code

Public Sub Calculate()
    Application.ScreenUpdating = False
    Application.CalculateFull
    Application.ScreenUpdating = True
End Sub

If I install both macros in a standard module in the workbook, it works fine. However, if I install the same code in a standard module in the Add-In, the first macro executes and the command is added to the right mouse click menu but when I execute the "Calculate" command from the mouse I get the message that the "Calculate" macro can't be found.

Am I missing something? All other macros run fine from the Add-In.

Thanks for your help.
John

*** I just discovered that the Add-In code DOES work in Excel 2007 but refuses to work in Excel 2000; any workaround you're aware of?