Gifting of The Witcher 3: Wild Hunt temporarily unavailable (fix in progress)
Due to a very large number of fraudulent transactions coming in, we have had to disable the gifting option for three items: The Witcher 3: Wild Hunt, The Witcher 3: Wild Hunt Expansion Pass, and The Witcher 3: Wild Hunt - Game + Expansion Pass.
We are working to clarify the problem and prevent further fraudulent transactions from being made.
We will make gifting possible once more as soon as this issue is resolved.
Make sure that your Windows user account has Administrator privileges.
Ideally, you should make sure that User Account Control is disabled in your operating system. To do this, go to Start -> Control Panel -> User Accounts and Family Safety -> User Accounts -> Change User Account Control settings. Move the slider to the lowest position ("Never notify") and click OK.
At the very least, launch the installer by right-clicking its shortcut and selecting "Run as Administrator". You should keep in mind, though that UAC can cause problems in a lot of applications, especially games, and therefore disabling it is preferable for most users in the long term.