Trouble grouping shapes in Word VBA

This is driving me crazy.  It seems so easy, but I am obviously missing something.  I have a macro that lets the user select one or more photos, provide a caption, and then it is supposed to groups the photos, put the caption under the group, then group the caption with the grouped photos, so they can all be moved as one unit.

Everything works fine until the very last line of the macro.  It gives me an error saying "grouping is disabled for the selected shapes."  

Sub captionselectedphoto(control As IRibbonControl)

Dim shapesselected As Integer
Dim photos2caption As ShapeRange
Dim phototitle As String

shapesselected = Selection.ShapeRange.count

If shapesselected = 0 Then
    MsgBox "Please select one or more photos to caption, then try again"
    Exit Sub
End If

Set photos2caption = Selection.ShapeRange

If photos2caption.count > 1 Then photos2caption.Group
Application.ScreenRefresh

phototitle = InputBox("Photo title?")

Selection.InsertCaption Label:="Figure", TitleAutoText:="", _
    Title:=": " & phototitle, Position:=wdCaptionPositionBelow, ExcludeLabel:=0

Set captionbox = ActiveDocument.Shapes(ActiveDocument.Shapes.count)

MsgBox photos2caption.Name  'returns "Group 20"
MsgBox captionbox.Name      'returns "Text Box 9"

ActiveDocument.Shapes.Range(Array(photos2caption.Name, captionbox.Name)).Group

End Sub

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As you can see, I stuck in a couple msgboxes near the end to tell me the shape names.  The return the expected names.  What is most maddening is that I can run this test macro and it does exactly what I want:

ActiveDocument.Shapes.Range(Array("Group 20", "Text Box 9")).Group

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This is what I'm aiming for.  Is there something wrong with my syntax?  Can I not put variables in the array statement like this?  What am I doing wrong?