There are times when uninstalls that are .msi based do not complete fully and when that happens it can be a pain. If you happen to know all the system registry entries, system files, and settings then you could dig through and remove these one at a time.
The easiest solution is to simply use the program install and uninstall troubleshooter from Microsoft as it is designed to help with failed uninstallations or installs.
Here is the link.