Sphero TwoPhonesOneBall sample compiler error

Question

I imported the samples of Sphero-Android SDK to my workspace. TwoPhonesOneBall project gives compiler errors. In ConnectionActivity.java class, the following imports cannot be resolved.

//...some imports

import orbotix.multiplayer.LocalMultiplayerClient;
import orbotix.multiplayer.MultiplayerControlStrategy;
import orbotix.multiplayer.MultiplayerGame;
import orbotix.multiplayer.RemotePlayer;

//...imports

How can I fix it? Since these classes don't exist, I didn't come up with a solution. I searched the net but I couldn't find similar problem. By the way,the same problem also occurs in MultiplayerLobby application.