I'm not a dev,
but this line
<code>MarkUpgrade() called on a non-upgrable pkg: 'ubuntu-desktop' ERROR:root:IOError in cache.commit(): 'Failed to fetch</code>
Seems to be where it choked.
Did you have ubuntu-desktop installed before you did a dist-upgrade?
I'm not a dev,
but this line
<code>MarkUpgrade() called on a non-upgrable pkg: 'ubuntu-desktop'
ERROR:root:IOError in cache.commit(): 'Failed to fetch</code>
Seems to be where it choked.
Did you have ubuntu-desktop installed before you did a dist-upgrade?