"You cannot install this product because another version is already installed."

Trying to re-install DVD Corel GS X8 after trying Corel GS 2018. I uninstalled Corel GS 2018, and then manually deleted all Corel directories in (1) Roaming, (2) Program Files, (3) Program Files X86, and (4) Program Data. Then I did a complete cache dump (CCleaner) and rebooted.

Tried again to install DVD of Corel GS X8, but keeps giving me the error "You cannot install this product because another version is already installed."

Clearly, I'm missing some old Corel files that need to be deleted. Help!!