Bug#645713: [WORKAROUND FIX] The following steps got me around this bug.

[Karl Fogel <kfogel@red-bean.com>]

I was stuck in the same place in a squeeze->testing upgrade -- doing
"apt-get upgrade" (and various other commands) got the error:

  E: Could not perform immediate configuration on 'libgstreamer0.10-0'.
  Please see man 5 apt.conf under APT::Immediate-Configure for details. (2)

I do not have a record of everything I tried to solve this, but most of
the attempts had no effect, because they either immediately ended in the
same error or offered me dependency-conflict resolution proposals that
were obviously unacceptable for one reason or another.

But then this sequence worked:

  # apt-get install gnome
  # apt-get -f install
  # apt-get -f dist-upgrade

Each step got some warnings, but none appeared too dangerous, so I went
ahead anyway.  I guess I got lucky, because my system is now finally on
up-to-date 'testing' distribution.  (You might want to finish off with
an 'apt-get autoremove'.)

YMMV,
-Karl