In some cases, players may receive an erroneous "Connection Lost" message when joining a public multiplayer match. Most of the time, this occurs when the player has attempted to join a match that is already full. Joining a new match with empty slots should allow you to successfully join a match.
If you continue to have issues connecting to multiplayer matches, please consult the following networking troubleshooting:
http://support.2k.com/entries/21980042-general-networking-troubleshooting