How did you add the XML?
It'd be easier if you would attach a small presentation with the macro, etc.
This is my XML. The attachment seems to work, so maybe it's one of your settings??
<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui">
<ribbon startFromScratch="false">
<tabs>
<tab id="customTab" label="Custom Tab">
<group id="customGroup" label="Custom Group">
<button id="updateProperties" label="updateProperties" imageMso="RecurrenceEdit" size="large" onAction="updatePropertiesCallback" />
</group>
</tab>
</tabs>
</ribbon>
</customUI>