I am new to GAE, I follow the instructions on http://code.google.com/eclipse/docs/install-eclipse-3.7.html. I got the installation and registration done pretty fast. But when I tried to build the helloWorld project in Eclipse, before I can do anything, Eclipse gives me an error says "java.lang.NoClassDefFoundError: com/google/appengine/tools/enhancer/Enhance" and it is very weird. Because when you expand the app engine sdk, you can easily find the Enhance class under related jar file. I also tried Enhance e = null; and it is working. It seems that my eclipse just cannot find it. I don't know why it is not working, I am using JDK1.6, I reinstall my eclipse and the google plugins, I even disabled my firewall. Please help!!!