Client lost its connection to server.
This happens to me too sometimes not sure why.
What MBP do you have, which specs in specific? Are you playing wireless or wired? If wireless, are you on a dual band router? Are you running any antivirus or firewall softwares?
Also, the next time you have this issue, open your console (/applications/utilities) and check for any errors or network messages. Watch for Mac address changes or anything else about your Internet connection.
Please post back with this info.
(I used to have a similar issue at random intervals, so trying to narrow down your specific problem. Tick, post your answers too, if you’d like.)