Hi Kate,
Looking at the URL string there I see both Pressflow and Pantheon variables being passed. It looks like the platform is in the way. I would suggest sending an email to the folks at Pantheon and/or Pressflow to get some help. I'm not sure what your technical expertise is, but Pressflow is a flavor of Drupal and Pantheon is a hosting service for Drupal. They appear to be adding variables to the URL, which probably isn't necessary.
Just my guess.
John
