8000FFFF - Generic Unexpected error  

Could be due to corruption in the registry values -
"PendingXmldentifier"
"NextQueueEntryIndex"
"AdvancedInstallersNeedResolving"
under the registry key: HKLM\Components.

1. Click on Start and in the Search box type in regedit
   
2. A new program will be listed in the same window. Now right click the regedit program and then select the option run as administrator.
   
3. Navigate to HKLM\COMPONENTS - look to see if these values exist under
   the COMPONENTS key:

PendingXmldentifier
NextQueueEntryIndex
AdvancedInstallersNeedResolving

4. If they exist, then delete the three values.

NB: Before deleting the anything in the registry, make sure you back up the keys - click the File option on the main toolbar, in the drop down menu select Export Select All in the Export Registry File dialog box.

Give the file a name, then click the Save button

If something goes wrong, then all you have to do is click on the File option on the main registry editor toolbar and then select Import

Disclaimer: Modifying the registry can cause serious problems that may require you to reinstall your operating system. Use the information provided at your own risk.

5. Restart the computer.

You receive error code 8000FFFF when you click "Check for Updates" in the Windows Update Control Panel item on a Windows Vista-based computer
http://support.microsoft.com/kb/946414

The error can also occur if -

• The relevant Windows Update services stop working.
• The temporary folder of Windows Update has been corrupted.
• Windows Update Agent does not work.
• A Third party program is affecting the WU Service (such as anti-spyware programs, Internet/web accelerators, Firewall/Anti-Virus programs) or the downloaded file/update is corrupt.

Suggestions:

1. Make sure the services are running.
   
   Click Start, type services.msc in the Start Search box and press Enter.
   
   In the right pane, check the following three services have been started:
   
   Background Intelligent Transfer Service (BITS)
   Windows Event Log
   Windows Update
   
   If they haven't been started, then start them one by one.
   
   
2. If the Temporary folder of Windows Update has been corrupted then it is suggested that you rename the SoftwareDistribution folder to whatever you like. This will take care of any corrupted downloaded files.  
   
   
3. If it's the Windows Update Agent that is not working -
   
   Click one of the following links as appropriate for the operating system.
   
   x86-based versions of Windows - download the WindowsUpdateAgent30-x86.exe package now.
   http://go.microsoft.com/fwlink/?LinkID=91237
   
   x64-based versions of Windows - download the WindowsUpdateAgent30-x64.exe package now.
   http://go.microsoft.com/fwlink/?LinkID=91238 

Note: I have read that this file cannot be launched directly from the system root directory therefore select a drive where Windows Vista is not loaded (perhaps a flash drive).

To install the Windows Update Agent, click Start, click Run, and type: "D:\WindowsUpdateAgent30-x86.exe /wuforce" (without quotations) and then press Enter to install the Windows Update Agent. Note that "D" for example the Flash Drive you have saved the Windows Update Agent to.

Also note that there is a space between "D:\WindowsUpdateAgent30-x86.exe" and "/wuforce"