Lost connexion to session

hi,
Every time I connect to a server I am disconnected and I get the message 'you have lost connection to the session' after 1 minute of play.
My internet connection is more than sufficient and I have no other connection problems with other games.
I saw on the steam forum (which I don't use) that some people have had this problem for several weeks but I didn't have any yesterday.

What's going on? When will this problem be resolved?
knowing that I bought the game less than a week ago I find that it makes a very bad impression..