Error Code Sheep may occur when players attempt to join a Fireteam in which any member has not updated to the latest version of Destiny. To resolve this issue, please close and restart Destiny to initiate your update.
If your console fails to update your Destiny application automatically, you may need to initiate the update manually. For more information on updating Destiny manually, please see: Updating Destiny Guide.
If all players in your Fireteam are playing the latest version of Destiny, please try to resume your activity.