IMPORTANT ANNOUNCEMENTS AND HOT TOPICS:
GOG Galaxy - troubleshooting and useful informationThe Witcher 3: Wild Hunt - buying as a gift temporarily unavailable (fix in progress)The Witcher 3: Wild Hunt - downloading, redeeming and installing FAQThe Witcher 3: Wild Hunt - Nvidia code FAQ
If you're experiencing problems with the re-installer, after applying your unique multiplayer key, try changing its compatibility setting to Windows XP (Service Pack 3).
To do this, right-click the re-installer, and select Properties -> Compatibility -> Run This program in compatibility mode for -> Windows XP (Service Pack 3). Afterwards, confirm with OK and try launching the re-installer now.