1.4 doesn't work? First Strike is now on 1.5 and has been since August last year. That could be your problem right there MaGlas.
Not sure what is going on with your situation Darcan, the message you are getting sounds like you might have tried to get on while the server was set up for testing, as there are no custom maps that come with 1.5. Try again now, as the server is definitely set up for public play at the moment. If you still have the same message it could be a Punkbuster issue, try updating that to see if that helps.