lol! this must be the third time I see a thread of this kind.
When u suddenlly loose connection to internet u get kicked out of the server cuz u cant connect. However u havent manually exit that server. Thats why, even thought u r not playing, the game still thinks u r IN the game. As a result u cant connect again cuz ur serial key, meaning the CD, is in "use" and its impossible to have twice the same serial number online. EVEN IF IT COMES FROM THE SAME IP ADRESS! So, what u have to do is wait until the game finishes and the server refreshes again so it notices u r not online. That way ur serial code is free again to join any server. If u loose connection while playing on s1, that might take a while cuz games are pretty long.
Hope it help!