I'm trying to add a sidebar gadget to Gmail using the guidance given in https://developers.google.com/gmail/sidebar_gadgets. To get started, I've taken a copy of the Hello World file, changed the text a bit and placed it in http://bachtrack.com/mygooglegadget.xml. I've added it to the list of gadgets in my Gmail settings, as specified - it's visible on the settings page.
Trouble is, nothing else happens at all. There's no visible gadget anywhere in my sidebar as a result of this, in any of a variety of screens.
What am I doing wrong? Here's the code - I really don't think I changed anything other than the text, and it appears to parse OK...
<?xml version="1.0" encoding="UTF-8" ?>
<Module>
<ModulePrefs title="Google gadget example from Bachtrack" />
<Content type="html">
<![CDATA[
Hello from my Bachtrack Gmail gadget!
]]>
</Content>
</Module>
By the way, I think this is the same as the unanswered https://stackoverflow.com/questions/21378334/gmail-gadget-doesnt-appear-sidebar but I'm posting it separately to include the tag google-bigquery.