FF7 Game Converter requires an unmodified version of FF7 (new or old release).
If you have a Re- or Steam-Release and have used Bootleg before, it is maybe necessary to rid the registry of unnecessary keys.
Before using FF7 Game Converter you need a volume labeled "FF7DISC1", "FF7DISC2" or "FF7DISC3" (for the Re- or Steam-Release it is enough to relabel a USB stick)