Can't install Corel x6 (another version already installed?)

Hi,

I'm having problems trying to install Corel x6 on Windows 8. I have previously had trial versions for x6 and x7 installed but these are uninstalled and whenever I try and run the installer I get the message:

The installation was not completed

Your system has not been modified. To complete installation at another time, please run setup again.

You cannot install the product because another version is already installed. To install this product, you must first uninstall the existing version. Click Finish to quit the setup.

I have tried creating a new user account (with admin privileges), i've tried deleting all entries for Corel in the registry as well as checking there are no letters in the 'zone' section with in the registry - all with firewall and antivirus and popups turned off, i've also checked I have .net4 installed -  all with no luck.

Does anyone have any ideas why I can't install it?

Thanks
James