java.lang.IllegalArgumentException: Invalid ClassPath root: file:/tmp/JA1/build/classes/. The root must be a folder.
   at org.netbeans.api.java.classpath.ClassPath$Entry.getRoot(ClassPath.java:734)
   at org.netbeans.api.java.classpath.ClassPath.createRoots(ClassPath.java:283)
   at org.netbeans.api.java.classpath.ClassPath.getRoots(ClassPath.java:266)
   at org.netbeans.modules.java.source.ant.ProjectRunnerImpl.computeProperties(ProjectRunnerImpl.java:230)
   at org.netbeans.modules.java.source.ant.ProjectRunnerImpl.execute(ProjectRunnerImpl.java:119)
   at org.netbeans.api.java.project.runner.JavaRunner.execute(JavaRunner.java:273)
   at org.netbeans.modules.java.j2seproject.J2SEActionProvider.bypassAntBuildScript(J2SEActionProvider.java:1285)
   at org.netbeans.modules.java.j2seproject.J2SEActionProvider.access$1200(J2SEActionProvider.java:141)
   at org.netbeans.modules.java.j2seproject.J2SEActionProvider$1Action.run(J2SEActionProvider.java:462)
   at org.netbeans.api.java.source.ui.ScanDialog.runWhenScanFinished(ScanDialog.java:153)
   at org.netbeans.modules.java.j2seproject.J2SEActionProvider.invokeAction(J2SEActionProvider.java:538)
   at org.netbeans.modules.project.ui.actions.MainProjectAction.actionPerformed(MainProjectAction.java:163)
   at org.netbeans.modules.project.ui.actions.LookupSensitiveAction.actionPerformed(LookupSensitiveAction.java:170)
   at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
   at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
   at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
   at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
   at javax.swing.AbstractButton.doClick(AbstractButton.java:357)
   at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:809)
   at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:850)
   at java.awt.Component.processMouseEvent(Component.java:6267)
   at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
   at java.awt.Component.processEvent(Component.java:6032)
   at java.awt.Container.processEvent(Container.java:2041)
   at java.awt.Component.dispatchEventImpl(Component.java:4630)
   at java.awt.Container.dispatchEventImpl(Container.java:2099)
   at java.awt.Component.dispatchEvent(Component.java:4460)
   at java.awt.LightweightDispatcher.retargetMouseEvent(LightweightDispatcher.java:4577)
   at java.awt.LightweightDispatcher.processMouseEvent(LightweightDispatcher.java:4238)
   at java.awt.LightweightDispatcher.dispatchEvent(LightweightDispatcher.java:4168)
   at java.awt.Container.dispatchEventImpl(Container.java:2085)
   at java.awt.Window.dispatchEventImpl(Window.java:2478)
   at java.awt.Component.dispatchEvent(Component.java:4460)
   at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
   at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:137)
   at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
   at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
   at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
   at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
   at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)