I'm using the latest forge and I have the same problem. It seems to me that the forge server jar isn't loading the launchwrapper library as it should. Manually setting the classpath gives me another error. Probabbly because I forgot to include some other libraries.
Hello,
Could you please change "python" to "python2" in the *NIX build script? It's not that big of a problem for personal use, but it breaks mod build scripts.