You can still play though - it just doesn't save the stats.
For new people here's how to play online:
Register here : http://www.burbworld.com/fs2netd/register.php
Start a multiplayer game from the pilot select screen
Go to the multiplayer options, and fill in your new login details to the PXO area :
^ Select TCP to connect to the new opensource server or IPX and enter an IP to connect to a private (friend's hosted) game.
Warning about hacked tables currently appear, but they do not affect the game itself, just ok them.