Maybe I'm missing something, but this should be working...

Private WithEvents objCommandBarButton As CommandBarButton

Private Sub Workbook_Open()
Dim obkCommandbars As CommandBars
Dim objCommandBar As CommandBar
Dim objCommandBarControl As CommandBarControl

' Create a menu command on the "Tools" menu.
objCommandBars = Me.Application.CommandBars("Tools")
objCommandBar = objCommandBars.Item("Tools")

' Make sure menu command doesn't already exist.
For Each objCommandBarControl In objCommandBar.Controls
If objCommandBarControl.Caption = "Perform Metric conversion..."
Then
objCommandBar.Controls.Item("Perform Metric
conversion...").Delete
End If
Next objCommandBarControl

objCommandBarButton = objCommandBar.Controls.Add(msoControlButton)

With objCommandBarButton
.Caption = "Perform Metrics Conversion..."
.Style = msoButtonCaption
.Tag = "Perform Metrics Conversion..."
.OnAction = "!<Magic_Metrics.Connect"
.Visible = True
End With
End Sub

Thanks,
Jody W