My suggestion to reinstall the 1.4.2 was because, from your first post, it seemed your existing 1.4.2 version install had an issue which prevented the proper uninstall, and this should have fixed by reinstalling the 1.4.2 version and they Uninstalling it again, so the GSX installer could proceed.
Right now, the SODE website hasn't been updated yet, so the only place you can find version 1.5.0, is in the GSX installer.
Are you SURE your installed version that couldn't be uninstalled was 1.4.2 and not, for example, 1.5.0 already, which WAS successfully installed by GSX after all ?