Adding on to what was already stated above by the helpful floofs.
Make sure you keep the tab up and running while you're playing the game as well as the browser.
Make sure you're internet is good and running and try to avoid really crowded places just in case ( that is, if your internet can't handle it ).
Check your Rendering System. Maybe you need to change it. Do so by going to options, Video , Rendering Systems and maybe that'll help if the problem persists. ( Correct me if I'm wrong by the way ).
Hope The Issue Gets Resolved Soon. Good Luck ^^
Also, try taking a look at THIS (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=54258.0) link.
In case you weren't aware of the login tab, you can find that there and it will explain how to use it.
Be sure not to minimize the tab, only run it in the background behind your game to keep the game running.
Also, be sure to wait a few seconds before logging in in-game.