I'm not sure this is a bug, but I can't explain why it's failing!

I have two private blogs within a site, and I'm trying to bring them together in one feed manager as described here https://www.mojoportal.com/using-the-blog-feed-in-feed-manager using the InternalFeedSecurityBypassKey hack.

I have added the app setting with the guid and I can access both blogs via direct URL, by adding &g={my guid} to the feed link URL.

However the feed manager displays items from one blog but not the other, and we see this in the system log:

2015-02-05 13:05:02,715 ERROR 62.197.51.164 - en-GB - /developers-blog - mojoPortal.Web.FeedUI.FeedCache - There was a problem trying to read the feed for url https://www.esdm.co.uk/Blog/RSS.aspx?p=179~151~-1.  Ignoring.
System.Xml.XmlException: Data at the root level is invalid. Line 1, position 1.
   at System.Xml.XmlTextReaderImpl.Throw(Exception e)
   at System.Xml.XmlTextReaderImpl.Throw(String res, String arg)
   at System.Xml.XmlTextReaderImpl.ParseRootLevelWhitespace()
   at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
   at System.Xml.XmlTextReaderImpl.Read()
   at System.Xml.XPath.XPathDocument.LoadFromReader(XmlReader reader, XmlSpace space)
   at System.Xml.XPath.XPathDocument..ctor(TextReader textReader)
   at Argotic.Common.SyndicationEncodingUtility.CreateSafeNavigator(String xml)
   at Argotic.Common.SyndicationEncodingUtility.CreateSafeNavigator(Stream stream, Encoding encoding)
   at Argotic.Common.SyndicationEncodingUtility.CreateSafeNavigator(Stream stream)
   at Argotic.Common.SyndicationEncodingUtility.CreateSafeNavigator(Uri source, ICredentials credentials, IWebProxy proxy, Encoding encoding)
   at Argotic.Syndication.GenericSyndicationFeed.Load(Uri source, ICredentials credentials, IWebProxy proxy, SyndicationResourceLoadSettings settings)
   at Argotic.Syndication.GenericSyndicationFeed.Create(Uri source, ICredentials credentials, IWebProxy proxy, SyndicationResourceLoadSettings settings)
   at mojoPortal.Web.FeedUI.FeedCache.GetRssFeedEntries(Int32 moduleId, Guid moduleGuid, Int32 entryCacheTimeout, Int32 maxDaysOld, Int32 maxEntriesPerFeed, Boolean enableSelectivePublishing)

The XML from the "bad" feed, when accessed directly, starts:

 <?xml-stylesheet type="text/css" href="https://www.esdm.co.uk/Data/style/rss1.css" ?> <?xml-stylesheet type="text/xsl" href="https://www.esdm.co.uk/Data/style/rss1.xsl" ?>
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:itunes="http://www.itunes.com/dtds/podcast-1.0.dtd">
  <channel>
    <title>Developers Blog</title>
    <link>https://www.esdm.co.uk/developers-blog</link>
    <description />
    <docs>http://www.rssboard.org/rss-specification</docs>
    <generator>mojoPortal Blog Module</generator>

Any idea why it could be choking?

mojoPortal Version 2.4.0.4 MSSQL
Operating System Microsoft Windows NT 6.0.6002 Service Pack 2
ASP.NET Info v4.0.30319 Running in Full Trust