Wii U USB Helper communicates over HTTP (port 80) and HTTPS (443). Some antivirus software quarantines the key download because it recognizes the pattern of piracy tools. Temporarily disable your antivirus or add USB Helper to the exclusion list.
When you first launch the software, it will prompt you for a website address to fetch game data. Use these current community-maintained URLs: title keys for wii u usb helper upd