The GS-911 Diagnostics PC App's installer is Web-based and uses session cookies for authentication against our cloud servers. If cookies are disabled on your Windows PC you will see an error message "Download error: Unauthorized (401)" after validation has been completed when trying to install:

Please go to "Control Panel -> Internet Options -> Privacy -> Advanced" and ensure that all cookies are enabled:

Apply, then retry using the GS-911 Diagnostics installer.