Sometimes (could not yet find a reliable way to reproduce it) I get an NPE when
running my main project:

java.lang.ArrayIndexOutOfBoundsException: 2 >= 2
	at java.util.Vector.elementAt(Vector.java:431)
	at javax.swing.JTabbedPane.getComponentAt(JTabbedPane.java:1201)
	at javax.swing.JTabbedPane.getSelectedComponent(JTabbedPane.java:637)
	at
org.netbeans.core.output2.ui.AbstractOutputWindow.remove(AbstractOutputWindow.java:136)
	at org.netbeans.core.output2.Controller.close(Controller.java:557)
	at org.netbeans.core.output2.Controller.performCommand(Controller.java:1069)
	at org.netbeans.core.output2.OutputWindow.eventDispatched(OutputWindow.java:316)
	at org.netbeans.core.output2.IOEvent.dispatch(IOEvent.java:255)
	at org.netbeans.core.output2.NbIO.post(NbIO.java:217)
	at org.netbeans.core.output2.NbIO.post(NbIO.java:206)
	at org.netbeans.core.output2.NbIO.closeInputOutput(NbIO.java:67)
	at org.apache.tools.ant.module.run.TargetExecutor.execute(TargetExecutor.java:146)
	at
org.apache.tools.ant.module.api.AntTargetExecutor.execute(AntTargetExecutor.java:75)
	at
org.apache.tools.ant.module.api.support.ActionUtils.runTarget(ActionUtils.java:66)
	at
org.netbeans.modules.java.j2seproject.J2SEActionProvider$1.run(J2SEActionProvider.java:204)
	at
org.netbeans.modules.javacore.internalapi.JavaMetamodel.invokeAfterScanFinished(JavaMetamodel.java:209)
	at
org.netbeans.modules.java.j2seproject.J2SEActionProvider.invokeAction(J2SEActionProvider.java:214)
	at
org.netbeans.modules.project.ui.actions.MainProjectAction.actionPerformed(MainProjectAction.java:91)
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1984)
	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2307)
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:377)
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:232)
	at
javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
	at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:231)
	at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:231)
	at java.awt.Component.processMouseEvent(Component.java:5999)
	at javax.swing.JComponent.processMouseEvent(JComponent.java:3203)
	at java.awt.Component.processEvent(Component.java:5764)
	at java.awt.Container.processEvent(Container.java:1984)
	at java.awt.Component.dispatchEventImpl(Component.java:4407)
	at java.awt.Container.dispatchEventImpl(Container.java:2042)
	at java.awt.Component.dispatchEvent(Component.java:4237)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4248)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3912)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3842)
	at java.awt.Container.dispatchEventImpl(Container.java:2028)
	at java.awt.Window.dispatchEventImpl(Window.java:2300)
	at java.awt.Component.dispatchEvent(Component.java:4237)
[catch] at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
	at
java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
	at
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

Once this has happened, I cannot use any of project menu items (Build, Clean,
Compile etc) and I need to restart the IDE

Happened with 5.5 dev build from Mai 22nd and May 25th

It could be related to running JUnit tests before, but I'm not sure