L4D2: Connection Failed after 10 Retries [FIX]
Straight to the point.
Solution 0: Restart PC and Internet Modem.
Solution 1: Go to Steam, Library, Left 4 Dead 2, Properties and add "+clientport 27006" without the quotations, to your launch parameters.
Restart steam and try again.
Solution 2: Go to Steam, Settings, Downloads and clear your download cache.