Comment 2 for bug 147328

I have just found a workaround.
The file DistUpgradeControler.py, used for upgrade, contains this code:
  if not item.IsTrusted:
   logging.error("pre-requists item '%s' is NOT trusted" % item.DescURI)
  return False
You can find this file under the folder /tmp/tmpXXXXXX that the upgrade manager create during install (XXXXXX change every time you try to execute the upgrade).
These are steps I used to exclude the control and to continue with the upgrade:
- launched an installation that failed with the error "is NOT trusted";
- changed the DistUpgradeControler.py row "return False" with "#return False";
- launched another installation and, immediately after "Distribution Upgrade" window appeared, replaced the file DistUpgradeControler.py (just created in the newly temporary dir /tmp/tmpYYYYYY) with the modified one, doing a command like this:
 mv /tmp/tmpXXXXXX/DistUpgradeControler.py /tmp/tmpYYYYYY
I hope this will help you to upgrade to Gutsy.
This worked for me!