You may receive Error 1721 when you try to remove programs by using Add or Remove Programs in Windows XP (891985)

RESOLUTION

To resolve this issue, perform the steps in the "Reregister the Windows Installer service" section. If you experience the issue after you perform these steps, you may also have to perform the steps in the "Run System File Checker" section.

Reregister the Windows Installer service

The Windows Installer service manages the installation and removal of programs. The service applies a set of centrally defined setup rules during the installation process. These setup rules define the installation and configuration of the installed program. Windows Installer uses the Microsoft installation engine to install or remove programs. If the registration of the Microsoft installation engine is corrupted, you may not be able to remove programs that you have installed by using Windows Installer. In that case, you have to unregister and reregister the Windows Installer service. To do this, follow these steps:

1. Start your computer in Safe mode. To do this, follow these steps:
   1. Restart the computer.
   2. After the BIOS information is displayed, press F8.
   3. Use the DOWN ARROW key to select Safe Mode, and then press ENTER.
   4. Use the UP ARROW key and the DOWN ARROW key to select your computer, and then press ENTER.
2. Log on to the computer as local administrator.
3. Click Start, click Run, type cmd.exe, and then click OK.
4. At the command prompt, type msiexec /unregister , and then press ENTER.
5. At the command prompt, type msiexec /regserver, and then press ENTER.
6. At the command prompt, type exit, and then press ENTER to close the command prompt.
7. Remove the software program from Add or Remove Programs.

Run System File Checker

The System File Checker (Sfc.exe) utility is used for scanning protected operating system files to verify their version and integrity. If System File Checker detects any operating system file with the incorrect file version, it replaces the corrupted file with a file that has the correct version from the Windows installation source files.

To use System File Checker, follow these steps:

1. Click Start, click Run, type cmd.exe, and then click OK.
2. At the command prompt, type sfc /purgecache, and then press ENTER.
   
   Note You may be prompted to provide Windows installation source files when you run the sfc /purgecache command. If the command is completed successfully, you will receive the following message:Windows File Protection successfully made the requested change.
3. At the command prompt, type sfc /scannow, and then press ENTER.
   
   Note This command may take several minutes to finish. You may also be prompted to provide Windows installation source files when you run the sfc /scannow command.
4. At the command prompt, type exit, and then press ENTER to close the command prompt.
5. Remove the software program from Add or Remove Programs.