you will have to have it in a folder too like
c:/halflife/esforces/
not just in half life dir
anouther thing is if u have renamed your hl.exe to something like "hl -console.exe" to run the console, esf may not be able to find it, in this case just make a copy of the exe, and name it to hl.exe i dont know if this will help, but thats a real why some ppl cannot use it.
if u have a ripped copy of half life theres not much anyone can do, so if u have one, go and buy it, and make sure you have the newest verson of hl too