I'm trying to do the custom ribbon example on pages 736 - 739 of John
Walkenbach's "Excel 2007 Power Programming with VBA".

I haven't been able to get the example files that should have been on
the cd (the cd just has a file that says it wasn't ready). So I'm
walking throught it manually. I'm getting the error "Excel cannot open
the file 'Excel 2007 Custom Ribbon Example.xlsm' because the file
format or file extension is not valid. Verify that the file has not
been corrupted and that the file extension matches the file format of
the file."

I've tried it with two new workbooks; same problem with both.

I do have "Show Add-In User Interface Errors" turned on.

Here's the VBA module text:

Sub CustomRibbonExample(control As IRibbonControl)
   MsgBox "ok"
End Sub

Here's the customUI.xml:

<customUI xmlns="http://schemas.microsoft.com/office/2006/01/
customui">
<ribbon>
<tabs>
<tab idMso="TabData">
 <group id="Group1" label="Custom">
   <button id="Button1"
     label="Custom Ribbon Example"
     size="normal"
     onAction="CustomRibbonExample"
     imageMso="HappyFace" />
 </group>
</tab>
</tabs>
</ribbon>
</customUI>

Here's what I added to the .rels:

<Relationship Type="http://schemas.microsoft.com/office/2006/
relationships/ui/extensibility" Target="/customUI/customUI.xml"
Id="12335" />

And here's the whole .rels:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Relationship Type="http://schemas.microsoft.com/office/2006/
relationships/ui/extensibility" Target="/customUI/customUI.xml"
Id="12335" />
<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/
relationships"><Relationship Id="rId3" Type="http://
schemas.openxmlformats.org/officeDocument/2006/relationships/extended-
properties" Target="docProps/app.xml"/><Relationship Id="rId2"
Type="http://schemas.openxmlformats.org/package/2006/relationships/
metadata/core-properties" Target="docProps/core.xml"/><Relationship
Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/
relationships/officeDocument" Target="xl/workbook.xml"/></
Relationships>

Any idea what's wrong?