How to Fix Error 1721

Re-register Windows Installer Service
1. Restart your computer and press the F8 key repeatedly as soon as you see the BIOS information on your screen. Pressing the F8 key allows you to access the 'Safe Mode' of your computer. Select 'Safe Mode' and hit 'Enter.'
2. Log on as 'local administrator.' Click 'Start' and select 'Run.' Type 'cmd.exe' in the 'Run' box and click 'OK.' This will open the DOS (command) prompt.
3. Un-register Windows Installer service by typing 'msiexec/unregister' at the command prompt and hit 'Enter.' Immediately re-register Windows Installer by typing 'msiexec/regserver' on the next command line and hit 'Enter.' Type 'Exit' to close out of the command prompt. You can now attempt to remove the program once again from 'Add or Remove Programs.'
Run System File Checker
4. Click 'Start,' select 'Run,' type 'cmd.exe' and click 'OK.' This brings up a DOS (command) prompt.
5. Type 'sfc/purgecache' at the command prompt and hit 'Enter.' At the next prompt, type 'sfc/scannow' and hit 'Enter.'
6. Type 'Exit' to close out the command prompt and once again attempt to remove the program from 'Add or Remove Programs.'