To resolve the issue that you're experiencing with the Da Vinci Disappearance DLC please follow the instructions below:
Next time you start the game you will be prompted to download an update. Your DLC should now work.
- Exit the game
- Go to My Xbox > System Settings > Memory > Hard-Drive
- Select the game
- Locate Title Update #5 and delete it.
- Go to My Xbox > System Settings > Memory > Hard-Drive
- Select the game
- Locate Title Update #5 and delete it.
Next time you start the game you will be prompted to download an update. Your DLC should now work.