I created an Excel Addin that appears in the UI, but whenever I click it it doesn't work.
Option Explicit
Public sheetscol As Collection, depshtnm
Public hasdeps As Boolean
'***********************************
'*finds the external dependencies of the cell, and places them in the 'sheetscol' collection
'***********************************
Sub depfinder_eventhandler(control As IRibbonControl)
    depfinder
End Sub
'--------------
Sub depfinder
 ...
End sub
This is the XML CustomUI:
<customUI xmlns="http://schemas.microsoft.com/office/2006/01/customui"
  xmlns:m="MattSinSpace">
    <ribbon>
        <tabs>
            <tab idQ="m:MattTab" label="Matt Tools" insertAfterMso="TabHome">
                <group idQ="m:migration" label="migration tools">
                    <button idQ="m:DepFinderButton1" label="Highlight Dependencies" size="large"
                     onAction="depfinder_eventhandler"                         imageMso="HappyFace" />
        </group>
                <group idQ="m:RS1" visible = "false"/>
            <group idQ="m:RS2" visible = "false"/>
            </tab>
        </tabs>
    </ribbon>
</customUI>
I'm pretty amateurish at making add-ins, and I've been using this page to help me out:
http://erpcoder.wordpress.com/2012/05/30/how-to-create-a-custom-ribbon-addin-for-excel-2010/
It appears that things are fine, in my code and my UI, the only difference is that I've included the namespace.
 
     
    