Steps to do in order to get a clean uninstall:
1. Go to the "Usefull Links" Section up in that page and download MCPR.exe, save it in your Desktop
2. Reboot PC and during rebooting press F8 key to go to Boot Options -> Boot in Safe Mode
3. Go to Control Panel and uninstall the product.
4. Reboot (normal or safe mode), run MCPR.exe
5. Reboot and clean folders:
5.1. C:\\Program Files\McAfee - delete everything inside.
5.2. C:\\Program Data\McAfee - delete the whole folder.
5.3. C:\\Users\YourUsername\Appdata\Local\Temp - delete everything which you can identify as a McAfee folder.
6. Reboot again and proceed to a new installation or whatever you need.
Another solution of your problem might be to update your Java. Very frequently the problems you described are related to this.
The latest version of Java you can find at Java.com, be sure to uninstal previous versions if installer doesn't require to.
Another solution that might be useful is to register the .dll files used.
Try these commands:
Go to Start->Run and type RESPECTING the spaces:
1. regsvr32 jscript.dll
2. regsver32 vbscript.dll
P.S. I assume that you have administrator rights.