We're rolling out Patch 1.1.2.0, to fix the problems we've been having with joining multiplayer lobbies.
Lobbies between versions are incompatible, so if there's a mixture of pre- and post-patch participants in a lobby, the multiplayer session will never start. Please be sure to patch your game to the latest version as soon as possible, and help spread the word to your pals. See the Project CARS forums for more details.