java.lang.AssertionError
        at org.netbeans.modules.form.layoutdesign.LayoutModel.addInterval(LayoutModel.java:319)
        at org.netbeans.modules.form.layoutdesign.LayoutDesigner.duplicateSequentially(LayoutDesigner.java:1830)
        at org.netbeans.modules.form.layoutdesign.LayoutDesigner.duplicateLayout(LayoutDesigner.java:1716)
        at org.netbeans.modules.form.actions.DuplicateAction.duplicate(DuplicateAction.java:119)
        at org.netbeans.modules.form.actions.DuplicateAction.performAction(DuplicateAction.java:84)
        at org.openide.util.actions.NodeAction$DelegateAction$1.run(NodeAction.java:589)
        at org.netbeans.modules.openide.util.ActionsBridge.implPerformAction(ActionsBridge.java:83)
        at org.netbeans.modules.openide.util.ActionsBridge.doPerformAction(ActionsBridge.java:64)
        at org.openide.util.actions.NodeAction$DelegateAction.actionPerformed(NodeAction.java:585)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2015)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2338)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
        at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
        at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:829)
        at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:873)
        at java.awt.Component.processMouseEvent(Component.java:6279)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3311)
        at java.awt.Component.processEvent(Component.java:6044)
        at java.awt.Container.processEvent(Container.java:2084)
        at java.awt.Component.dispatchEventImpl(Component.java:4639)
        at java.awt.Container.dispatchEventImpl(Container.java:2142)
        at java.awt.Component.dispatchEvent(Component.java:4465)
        at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4664)
        at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:4327)
        at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:4257)
        at java.awt.Container.dispatchEventImpl(Container.java:2128)
        at java.awt.Window.dispatchEventImpl(Window.java:2612)
        at java.awt.Component.dispatchEvent(Component.java:4465)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:618)
        at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:125)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:286)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:201)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:191)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:186)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:178)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:139)