This is such an old and dead issue, and I'm with Deeival on this one. I have had connection fail problems ever since I got Ostfront, and I bought Ostfront a week after it was released. This issue will never get solved IMHO, but tips are useful anyways.
I get it at least once a day, and if I get it more than that, just close and restart steam and it shouldn't do it anymore. The only time it is a real problem is when you are on a horrible server. I believe server settings are the sole reason for this error; as well as playing in oversea servers. Their are some servers I have been on, and you will see people just drop like flies and come back. Make sure you have your server tweaked, running on a proper machine, not running more slots than the server can hold and less players will get the issue on that server.