I receive Synchronization failed when playing Assassins Creed 4. What should I do?
This happens because the client is not updated to the latest version. You will need to use the Uplay's built-in menus to check for updates. Go to Help > Check for updates. Apply the available updates for the client and then reboot the computer. After it boots, start the game again and it should work. This error is related to the achievements.
Direct download URL: https://static3.cdn.ubi.com/orbit/launcher_installer/UplayInstaller.exe