Location of previous installation check

Hi,

I had a version of the FortiClient VPN installed, which was recently uninstalled. Now, every time I try to install the FortiClient again, a message pops up saying: "A more recent version of this product is already installed", even though it is NOT. Does anybody know where this check is performed so I can fix the problem? The installer just won't go further than the initial step before this check is performed and passes.