To resolve Windows Update error 8000FFFF, try the following steps:
1. Launch REGEDIT
2. Go into HKLM\COMPONENTS, and check if these three values exist under the COMPONENTS key:
PendingXmldentifier NextQueueEntryIndex AdvancedInstallersNeedResolving3) Providing they do exist, back up the Components key, then delete the three above values.
4) Restart the computer, and Windows Update should now be working fine.