java.lang.IllegalArgumentException: Project JavaApplication1 is not open and cannot be set as main. at org.netbeans.modules.project.ui.OpenProjectList.setMainProject(OpenProjectList.java:480) at org.netbeans.modules.project.ui.actions.OpenProject.actionPerformed(OpenProject.java:119) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318) 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:3240) 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(LightweightDispatcher.java:4248) at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:3912) at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:3842) at java.awt.Container.dispatchEventImpl(Container.java:2028) at java.awt.Window.dispatchEventImpl(Window.java:2405) at java.awt.Component.dispatchEvent(Component.java:4237) at java.awt.EventQueue.dispatchEvent(EventQueue.java:600) 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)