If you have a different client.dll make sure you've updated ESF and Steam/Half Life. That's simple stuff stated in the help section. If you can't find your Fmod.dll it usually means you need to reinstall ESF.
Just search for an updated version of CS/Half-Life/Steam and get that to fix the client.dll problem. If that doesn't work make sure you have ESF beta 1.1 and not 1.0 .
Closed. Seek further assistence in the stickies and the help forum. You should have been able to locate all of this in pre-existing threads. Search around next time you think up a question.