I know a lot of people have had this problem, Steam has been no help.This is what I have tried already. Solution: If you are experiencing this problem with Counter-Strike: Source or any of the other mods, please do the following. 1. Download this file: 2. Unrar haken.rar 3. Copy the file "steamclient.dll" to the ..\root\bin directory. The default path is C:\Program Files\Half Life 2\root\bin 4. Play the game as usual (run the play_CSS.bat or play_mods.bat on the desktop) but that didnt work for me maybe it will for you.I have also tried this: Get the dedicated server via Steam, start it once and then take the steamclient.dll from ...Steam\Steamapps\<Username>\source dedicated server\bin and place it in ...Steam\Steamapps\<Username>\counter-strike source\bin If there is one already, rename it or just replace it with the one the dedicated server. If there is none (as in my installation), just put in in there. That didn't work for me either but maybe it will help somebody out there. If anybody has anything better please let me know.