TFS Database Backup Failed : There is an error in XML document - but which Doc?

Question

Our Nightly TFS 2012 backup has just started to fail. It also fails when run directly through TFS Express Administration Console.

Which file is the following error a

Answer 1

Dylan answered my original question as to where to find the unspecified xml file that was in error, but in case it helps anyone else...

The Backupsets.xml file was empty. Why this is I do not know... Attempting to configure backups through TFS Express Administration Console also failed with the same error, so I

1. Deleted the Backupsets.xml file altogether
2. Reconfigured Backups using the wizard - Now that it didn't find the xml file at all it created a new one.
3. Ran a full backup - which was sucessful. Hopefully the scheduled backups will now also work from now on.

NB The newly created Backupsets.xml file (Before the first full backup) :

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