At startup, the GUI does not show up. Instead, I get an "Exception window", 
with the following backtrace: 
 
java.util.ConcurrentModificationException 
	at 
java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449) 
	at java.util.AbstractList$Itr.next(AbstractList.java:420) 
	at 
org.netbeans.modules.javacore.jmiimpl.javamodel.LightAttrList$LightAttrListIterator.next(LightAttrList.java:444) 
	at 
org.netbeans.modules.javacore.jmiimpl.javamodel.FeaturesList$FeatureListIterator.next(FeaturesList.java:465) 
	at 
org.netbeans.modules.java.bridge.ObjectsCollection.getElements(ObjectsCollection.java:109) 
	at 
org.netbeans.modules.java.bridge.MethodsCollection.getMethods(MethodsCollection.java:76) 
	at 
org.netbeans.modules.java.bridge.ClassElementImpl.getMethods(ClassElementImpl.java:565) 
	at org.openide.src.ClassElement.getMethods(ClassElement.java:485) 
	at org.openide.src.ClassElement.hasMainMethod(ClassElement.java:802) 
	at 
org.netbeans.modules.jemmysupport.runinternally.RunInternallyAction.getSelectedMainClass(RunInternallyAction.java:204) 
	at 
org.netbeans.modules.jemmysupport.runinternally.RunInternallyAction.enable(RunInternallyAction.java:98) 
	at org.openide.util.actions.NodeAction.isEnabled(NodeAction.java:170) 
	at org.openide.awt.Actions$ButtonBridge.updateState(Actions.java:674) 
	at org.openide.awt.Actions$Bridge.addNotify(Actions.java:458) 
	at 
org.openide.awt.Actions$Bridge$VisL.propertyChange(Actions.java:496) 
	at 
java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:333) 
	at 
java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:270) 
	at java.awt.Component.firePropertyChange(Component.java:7159) 
	at javax.swing.JComponent.addNotify(JComponent.java:4470) 
	at java.awt.Container.addNotify(Container.java:2500) 
	at javax.swing.JComponent.addNotify(JComponent.java:4469) 
	at org.openide.awt.Toolbar.addNotify(Toolbar.java:568) 
	at java.awt.Container.addNotify(Container.java:2500) 
	at javax.swing.JComponent.addNotify(JComponent.java:4469) 
	at java.awt.Container.addNotify(Container.java:2500) 
	at javax.swing.JComponent.addNotify(JComponent.java:4469) 
	at java.awt.Container.addNotify(Container.java:2500) 
	at javax.swing.JComponent.addNotify(JComponent.java:4469) 
	at java.awt.Container.addNotify(Container.java:2500) 
	at javax.swing.JComponent.addNotify(JComponent.java:4469) 
	at java.awt.Container.addNotify(Container.java:2500) 
	at javax.swing.JComponent.addNotify(JComponent.java:4469) 
	at javax.swing.JRootPane.addNotify(JRootPane.java:680) 
	at java.awt.Container.addNotify(Container.java:2500) 
	at java.awt.Window.addNotify(Window.java:466) 
	at java.awt.Frame.addNotify(Frame.java:501) 
	at java.awt.Window.show(Window.java:513) 
	at java.awt.Component.show(Component.java:1300) 
	at java.awt.Component.setVisible(Component.java:1253) 
	at 
org.netbeans.core.windows.view.ui.MainWindow.setVisible(MainWindow.java:544) 
	at 
org.netbeans.core.windows.view.DefaultView.showWindowSystem(DefaultView.java:526) 
	at 
org.netbeans.core.windows.view.DefaultView.windowSystemVisibilityChanged(DefaultView.java:479) 
	at 
org.netbeans.core.windows.view.DefaultView.changeGUI(DefaultView.java:163) 
	at 
org.netbeans.core.windows.ViewRequestor.dispatchRequest(ViewRequestor.java:238) 
	at 
org.netbeans.core.windows.ViewRequestor.processVisibilityRequest(ViewRequestor.java:227) 
	at 
org.netbeans.core.windows.ViewRequestor.postVisibilityRequest(ViewRequestor.java:164) 
	at 
org.netbeans.core.windows.ViewRequestor.scheduleRequest(ViewRequestor.java:85) 
	at org.netbeans.core.windows.Central.setVisible(Central.java:74) 
	at 
org.netbeans.core.windows.WindowManagerImpl.setVisible(WindowManagerImpl.java:710) 
	at 
org.netbeans.core.windows.WindowSystemImpl.show(WindowSystemImpl.java:56) 
[catch] at org.netbeans.core.NonGui$3.run(NonGui.java:223) 
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209) 
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:461) 
	at 
java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242) 
	at 
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163) 
	at 
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157) 
	at 
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149) 
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:110) 
 
 
I see two possible ways how my default project might be different from 
most other projects: 
1) It uses a lot of generics. 
2) I use subversion, and develop the code on two different computers. 
   I notice that the files 
U    nbproject/nbproject/project.xml 
U    nbproject/nbproject/genfiles.properties 
   are different on the two different computers, and every time I check in 
   a version from the other computer, I see that those files are changed. 
   I don't know if this might result in the problem?