Description of problem:
I'm testing the fc12 alpha image. 
A new window poped up:
"An internal system error has occurred"

Version-Release number of selected component (if applicable):
rpm -qa yum*
yum-metadata-parser-1.1.2-13.fc12.i686
yum-3.2.23-13.fc12.noarch
yum-utils-1.1.22-3.fc12.noarch


How reproducible:
first occurance today I will see if it appears again

Steps to Reproduce:
1. wait for the automatic update check (yum) to occur
2.
3.
  
Actual results:
a new window pops up: "An internal system error has occurred"
containing the traceback of yumBackend.py

Expected results:


Additional info:

Traceback output:
Traceback (most recent call last):
  File "/usr/share/PackageKit/helpers/yum/yumBackend.py", line 2180, in get_updates
    ygl = self.yumbase.doPackageLists(pkgnarrow='updates')
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 1714, in doPackageLists
    for (n,a,e,v,r) in self.up.getUpdatesList():
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 715, in <lambda>
    up = property(fget=lambda self: self._getUpdates(),
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 595, in _getUpdates
    self._up = rpmUtils.updates.Updates(self.rpmdb.simplePkgList(), self.pkgSack.simplePkgList())
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 702, in <lambda>
    pkgSack = property(fget=lambda self: self._getSacks(),
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 538, in _getSacks
    self.repos.populateSack(which=repos)
  File "/usr/lib/python2.6/site-packages/yum/repos.py", line 277, in populateSack
    sack.populate(repo, mdtype, callback, cacheonly)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 164, in populate
    if self._check_db_version(repo, mydbtype):
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 222, in _check_db_version
    return repo._check_db_version(mdtype)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1220, in _check_db_version
    repoXML = self.repoXML
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1384, in <lambda>
    repoXML = property(fget=lambda self: self._getRepoXML(),
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1376, in _getRepoXML
    self._loadRepoXML(text=self)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1366, in _loadRepoXML
    return self._groupLoadRepoXML(text, ["primary"])
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1349, in _groupLoadRepoXML
    if self._commonLoadRepoXML(text):
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1195, in _commonLoadRepoXML
    result = self._getFileRepoXML(local, text)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 976, in _getFileRepoXML
    cache=self.http_caching == 'all')
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 754, in _getFile
    result = self.mediafunc(local = local, checkfunc = checkfunc, relative = relative, text = text, copy_local = copy_local, url = url, mediaid = self.mediaid, name = self.name, discnum = discnum, range = (start, end))
  File "/usr/share/PackageKit/helpers/yum/yumBackend.py", line 2863, in MediaGrabber
    manager = MediaManager()
  File "/usr/share/PackageKit/helpers/yum/yumMediaManager.py", line 101, in __init__
    raise NotImplemented
TypeError: exceptions must be classes or instances, not NotImplementedType