You cannot install some updates or programs in Windows XP

1. Click Start, click Run, type cmd in the Open box, and the click OK.
   
   Note On a Windows Vista-based computer, click Start, type cmd in the Start Search text box, right-click cmd.exe, and then click Run as administrator.
2. At the command prompt, type the following command, and then press Enter:
   ren %systemroot%\system32\catroot2\Edb.log *.tst

You can continue to use the Enable trusted publisher lockdown Group Policy setting, but you must first add the appropriate certificates to your Trusted Publishers certificate store. To do this, turn off the Enable trusted publisher lockdown Group Policy setting, install the appropriate certificates in your Trusted Publishers certificate store, and then turn the Enable trusted publisher lockdown Group Policy setting back on. To install the appropriate certificate for Microsoft Windows and Microsoft Internet Explorer product updates, follow these steps:  

1. Download the Microsoft product update that you want to install from the Microsoft Download Center, from the Windows Update Catalog, or from the Microsoft Update. 
   
   For more information about how to download product updates from the Microsoft Download Center, view how to obtain Microsoft support files from the Online Services Catalog .
   For more information about how to download product updates from the Windows Update Catalog, view how to download updates that include drivers and hotfixes from the Windows Update Catalog .
2. Extract the product update package to a temporary folder. The command-line command that you use to do this depends on the update that you are trying to install. View the Microsoft Knowledge Base article that is associated with the update to determine the appropriate command-line switches that you will use to extract the package. For example, to extract the 824146 security update for Windows XP to the C:\824146 folder, run Windowsxp-kb824146-x86-enu -x:c:\824146. To extract the 828750 security update for Windows XP to the C:\828750 folder, run q828750.exe /c /t:c:\828750.
3. Right-click the KBNumber.cat file from the product update package in the temporary folder you created in step 2, and then click Properties.
   
   Note The KBNumber.cat file may be in a subfolder. For example, the file may be in the C:\824146\sp1\update folder or in the C:\824146\sp2\update folder.
4. On the Digital Signatures tab, click the digital signature and then click Details.
5. Click View Certificate, and then click Install Certificate.
6. Click Next to start the Certificate Import Wizard.
7. Click Place all certificates in the following store, and then click Browse.
8. Click Trusted Publishers, and then click OK.
9. Click Next, click Finish, and then click OK.

To verify certificates in the certificate path for a Windows or Internet Explorer product update, follow these steps:

Step 1: Verify Microsoft certificates

To clear the temporary file and restart the hotfix installation or the service pack installation, follow these steps:

1. Click Start, click Run, type cmd, and then click OK.
2. At the command prompt, type the following commands. Press Enter after each command.
   net stop cryptsvc
   ren %systemroot%\System32\Catroot2 oldcatroot2
   net start cryptsvc
   exit
3. Remove all the tmp*.cat files in the following folders:
   
   %systemroot%\system32\CatRoot\{127D0A1D-4EF2-11D1-8608-00C04FC295EE}
   %systemroot%\system32\CatRoot\{F750E6C3-38EE-11D1-85E5-00C04FC295EE}
   
   If no files that start with "tmp" exist in this folder, do not remove any other files. The .cat files in this folder are necessary for installing hotfixes and service packs.
   
   Important Do not rename the Catroot folder. The Catroot2 folder is automatically recreated by Windows, but the Catroot folder is not recreated if the Catroot folder is renamed.
4. Delete all the oem*.* files from the %systemroot%\inf folder.
5. Restart the failed hotfix installation or service pack installation.

1. Click Start, click Run, type services.msc, and then click OK.
   
   Note On a Windows Vista-based computer, click Start, type services.msc in the
   Start Search box, right-click services.msc, and then click Run as administrator.
2. In the Services (Local) pane, right-click Automatic Updates, and then click Stop.
3. Minimize the Services (local) window.
4. Select all the contents of the Windows distribution folder, and then delete them.
   
   Note By default, the Windows distribution folder is located in the drive:\Windows\SoftwareDistribution folder. In this location, drive is a placeholder for the drive where Windows is installed.
5. Make sure that the Windows distribution folder is empty, and then maximize the Services (local) window.
6. In the Services (Local) pane, right-click Automatic Updates, and then click Start.
7. Restart the computer, and then run Windows Update again.