Yet another failing appcast

My app cast is behind a vpn server on a private site.

But I can get to the appcast without any issue once on VPN. It's included below

When I run, I simply receive the dialog:
Update Error! An error occurred in retrieving update information. Please try again later. (Cancel Update)
The log also adds: Sparkle Error (continued): An error occurred while parsing the update feed.

I've tried attaching a delegate class to the SUUpdater instance in the nib.
The delegate instantiates, but nothing in it is called.

I know the shared updater has the delegate attached because the awake from nib on the delegate class checks this:
-[UpdaterDelegate awakeFromNib] <-- <UpdaterDelegate: 0x12259d0>
-[UpdaterDelegate awakeFromNib] --- updater SUUpdater <apppath>
-[UpdaterDelegate awakeFromNib] --- delegate <UpdaterDelegate: 0x12259d0>
-[UpdaterDelegate awakeFromNib] -->

Calls from the app to [[SUUpdater sharedUpdater] checkForUpdateInformation];
Result in the same behaviour. No delegate methods called. No more details.

I'm really hoping that I don't have to build the sparkle code into the app to find out whats wrong.

Any notes very welcome.

-A

The appcast (with minor redactions is:)
<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0" xmlns:sparkle="http://www.andymatuschak.org/xml-namespaces/sparkle" xmlns:dc="http://purl.org/dc/elements/1.1/">
   <channel>
      <title>PROGRAM Change Log</title>
      <link>http://macbuildserver.OURCO.com/MacOS/PROGRAM.xml</link>
      <description>Most recent changes with links to updates.</description>
      <language>en</language>
  <!-- Now here's an example of a version with a weird internal version number (like an SVN revision) but a human-readable external one. -->
  <item>
   <title>Version 1.0 &alpha;7</title>
   <sparkle:releaseNotesLink>
    http://macbuildserver/MacOS/PROGRAM/1.0/2-a/007-365.html
   </sparkle:releaseNotesLink>
   <pubDate>Thu, 24 Mar 2011 15:45:28 -0400</pubDate>
   <enclosure
    url="http://macbuildserver/MacOS/PROGRAM/1.0/2-a/007-365/PROGRAM.zip"
    sparkle:version="1365"
    sparkle:shortVersionString="1.0α7"
    type="application/octet-stream"
    length="3009573"
    sparkle:dsaSignature="(64 chars)"
   />
  </item>
   </channel>
</rss>