How to Fix a 1721 Windows Installer Error
When using the "Add or Remove Programs" feature in the Windows operating system to remove a program, you may receive "Error 1721." This error indicates that there is a problem with the Windows Installer package. In order to correct this error and be able to remove programs you must re-register the Windows Installer service by using the command prompt feature within Safe mode. This process helps to fix any corrupted files that were a part of Windows Installer.
Restart your computer and press the “F8” key on your keyboard before Windows starts up.
Press the “down” arrow key on your keyboard to highlight the “Safe Mode” option. Press the “Enter” key on your keyboard.
Select your computer with the arrow keys and then press the “Enter” key. Your computer will then start in Safe mode and you’ll be prompted to log in as a local administrator.
Click on the “Start” button, then click “Run.” Enter “cmd.exe” into the “Open” field and then click on the “Open” button.
Enter “msiexec /unregister” into the command prompt and press the “Enter” key. Enter “msiexec /regserver” into the command prompt and press the “Enter” key.
Type “exit” into the command prompt and press the “Enter” key. The Error 1721 will be fixed and you can remove programs using the "Add or Remove Programs" feature.