I just read through the comments on this article and several people are having problems. Chris Stone mentions that you should have Dev Tools installed and also says that there is a December Dev Tools distribution available from connect.apple.com (free registration required)!
If you are having problems, don't just reinstall the Dev Tools that you have on cd-rom. Get the latest (one big download and install and then a smaller update). Hopefully this will help, but even if it doesn't everyone will be on working off the same page.