You must have got a bad download, most likely caused by the antivirus or firewall. Try all of these:
- Disable the antivirus and firewall while downloading the installer
- Delete the browser cache and restart it
- Remove this folder:
Documents\GSX_Installer
Download again the installer and try again. Be sure you don't have multiple copies of it in your Downloads folder. If you have them, remove them all and start again.
