You can receive a registration key for your Registry Cleaner only if you get in touch with McAfee Sales Department. If you want to remove the application from your computer you can use Add or Remove Programs feature:
For Windows XP or bellow you can go to Start > Control Panel > Add or Remove Programs. In the Currently installed programs box, click on the Registry Cleaner program and then click Remove. If you have Windows Vista or above you need to go to Start > Control Panel > Programs > Programs and Features. Select the Registry Cleaner application and click on Uninstall.
If this doesn't help, you can force the application to uninstall using Revo Uninstaller.
Also, if you need a registry cleaner for your computer, I suggest you use a free utility from Software Informer database.