Fedora :: Software Update - Internal System Error

I've upgraded from FC11 to FC12 32-bit (live CD to HD install). Now when I try to perform software updates it gives me an Internal System Error. I've clicked on more details and it gives me the following:

Code:
Error Type: <class 'yum.Errors.RepoError'>
Error Value: Error getting repository data for installed, repository not found
File : /usr/share/PackageKit/helpers/yum/yumBackend.py, line 3125, in <module> main()
File : /usr/share/PackageKit/helpers/yum/yumBackend.py, line 3122, in main
backend.dispatcher(sys.argv[1:])
File : /usr/lib/python2.6/site-packages/packagekit/backend.py, line 710, in dispatcher
self.dispatch_command(args[0], args[1:])
File : /usr/lib/python2.6/site-packages/packagekit/backend.py, line 657, in dispatch_command
self.update_packages(only_trusted, package_ids)
File : /usr/share/PackageKit/helpers/yum/yumBackend.py, line 1948, in update_packages
signed = self._is_package_repo_signed(pkg)
File : /usr/share/PackageKit/helpers/yum/yumBackend.py, line 1437, in _is_package_repo_signed
repo = self.yumbase.repos.getRepo(pkg.repoid)
File : /usr/lib/python2.6/site-packages/yum/repos.py, line 121, in getRepo
'Error getting repository data for $s, repository not found' $ (repoid)

Everything else seems to work, including all of the programs I've installed from non-Fedora sources i.e. DOSEmu, Adobe Flash plug-in and Cannon LBP-660 printer driver.