The title summarizes the situation pretty well. All of a sudden, starting today, I can't launch the game via the launcher's "Launch game" button. It launches fine from the "System" folder's Witcher.exe straight away.

Why the issue all of a sudden?

I've had a similar issue but with both the launcher and the 'witcher.exe'. I solved it by disabling any compatibility mode apart from Admin rights (it was set to Windows 7).