The most frequent cause of this error is the absence of the correct client files.
When launching via Steam or an older retail disc, the game tries to find the legacy "Ubisoft Game Launcher" (Uplay). Because this legacy client has been replaced by the modern Ubisoft Connect, the game fails to detect it and throws an error. The most frequent cause of this error is
Once installed, restart your PC and log in to your Ubisoft account. The most frequent cause of this error is