did u save the playlist after u edited it? i made this mistake....if u did i dont know what else u could do. u could try to listen to winamp while youre playing. just dl it at winamp. com (most likely, im not sure) then open it and put music in your playlist and load esf. some1 else could probably offer more help than me, but its just a suggestion.
EDIT: i just found this -
Issue: The mp3 music doesn't play, and/or you get an Wrong dll version error in the console.
Problem:The installer installs fmod.dll in the windows dir, instead of in the halflife dir, and there is an older version of fmod.dll in your halflife dir.
Fix: Copy fmod.dll from your windows dir to your halflife dir.
hope this works =)