Isn't that the message that comes up if you don't have the right mod installed?
Like clicking on a CS server when you only have Half-Life and TFC?
You're probably trying to join a ESF 1.3 Open Beta server when you only have ESF 1.2.3 (or the other way round)
dan_esf_fanatic said:
That error only happens in WON. You need to use Steam, ESF openbeta doesn't work with WON. You also need an original copy of Half-Life, then you can play.
If that was the case, he'd be pretty lucky to find an esf server??
EDIT: wait, I think you're right... this happened to me about a month ago when I couldn't log into Steam for about a week.. I reinstalled WON CS retail and put ESF on that instead, then accidentaly clicked find servers.