If you want to run v6 side-by-side with v5 then you should use install the Portable version of FileLocator Pro 6.5. The portable version will install to any folder and doesn't require administrator privileges to run. The only missing functionality (compared to a standard v6 install) will be Shell related functionality.
The installer technology used by FileLocator Pro changed from v5 to v6 and a regular install requires that v5 is first manually uninstalled before v6 can be installed. Any future normal installs will automatically uninstall the old version before installing the new version.