I create NetBeans Modules, then JFrame, then JTabbedPane, then add JPanel, the code generated has this line: aJTabbedPane.addTab(org.openide.util.NbBundle.getMessage(etc..); triggering compile error of package org.openide.util does not exist.
However, skipping the creation of NetBeans Modules and going to Java Class directly, the code generated has this line: aTabbedPane.addTab("title", aJPanel); which compiles ok.
I have not touched Ant.
In NetBeans modules the GUI builder expects that org.openide.util is available. It's quite unusual a real module would not have this dependency. Bug 196497 is about that the GUI builder should add the dependency automatically. For now you need to add it manually. So go to project properties, libraries, and add org.openide.util and also org.openide.util.lookup.
You can also turn off the automatic internationalization of the GUI form if you don't want it at all (see properties of the root node in Navigator - for opened form).
*** This bug has been marked as a duplicate of bug 196497 ***