After launching your game from the ESEA Client, you may see the following Valve Anti-Cheat error appear on the game's home page:
Some of your game files have been detected to have no signatures or
invalid signatures. You will not be allowed to join VAC secure servers.
Please verify your launch options, check correctness of your game
installtion, restart the game and try again.
This is due to the way the ESEA Client secures Counter-Strike and will not cause any problems while playing ESEA. If you wish to join a VAC secured server and do not want to play on ESEA, close your game and launch it from your Steam library instead of through the ESEA Client.