java.lang.IllegalArgumentException: Invalid ClassPath root: file:/home/comul/nb69/idari2/mhs-ejb/build/classes/. The root must be a folder.
   at org.netbeans.api.java.classpath.ClassPath$Entry.getRoot(ClassPath.java:734)
   at org.netbeans.api.java.classpath.ClassPath.createRoots(ClassPath.java:283)
   at org.netbeans.api.java.classpath.ClassPath.getRoots(ClassPath.java:266)
   at org.netbeans.api.java.classpath.ClassPath.findResource(ClassPath.java:409)
   at org.netbeans.modules.j2ee.persistence.action.UseEntityManagerAction.enable(UseEntityManagerAction.java:125)
   at org.openide.util.actions.NodeAction$DelegateAction.resultChanged(NodeAction.java:615)
Caused: java.lang.reflect.InvocationTargetException
   at sun.reflect.GeneratedMethodAccessor17.invoke(GeneratedMethodAccessor17.java:0)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
   at java.lang.reflect.Method.invoke(Method.java:597)
   at org.openide.util.WeakListenerImpl$ProxyListener.invoke(WeakListenerImpl.java:459)
Caused: java.lang.reflect.UndeclaredThrowableException
   at $Proxy2.resultChanged(.java:0)
   at org.openide.util.lookup.ProxyLookup$1Notify.run(ProxyLookup.java:176)
   at org.openide.util.lookup.ProxyLookup.setLookups(ProxyLookup.java:182)
   at org.openide.util.lookup.ProxyLookup.setLookups(ProxyLookup.java:122)
   at org.openide.explorer.DefaultEMLookup.updateLookups(DefaultEMLookup.java:134)
   at org.openide.explorer.DefaultEMLookup.propertyChange(DefaultEMLookup.java:166)
   at org.openide.util.WeakListenerImpl$PropertyChange.propertyChange(WeakListenerImpl.java:196)
   at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:339)
   at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:276)
   at org.openide.explorer.ExplorerManager$2.run(ExplorerManager.java:868)
   at org.openide.util.Mutex.doEvent(Mutex.java:1341)
   at org.openide.util.Mutex.readAccess(Mutex.java:348)
   at org.openide.explorer.ExplorerManager.fireInAWT(ExplorerManager.java:865)
   at org.openide.explorer.ExplorerManager$1AtomicSetSelectedNodes.fire(ExplorerManager.java:285)
   at org.openide.explorer.ExplorerManager.setSelectedNodes(ExplorerManager.java:296)
   at org.openide.explorer.ExplorerManager$1SetExploredContextAndSelection.run(ExplorerManager.java:384)
   at org.openide.util.Mutex.readAccess(Mutex.java:365)
   at org.openide.util.Mutex$1R.run(Mutex.java:1307)
   at org.openide.util.Mutex.doWrapperAccess(Mutex.java:1324)
   at org.openide.util.Mutex.readAccess(Mutex.java:354)
   at org.openide.explorer.ExplorerManager.setExploredContextAndSelection(ExplorerManager.java:411)
   at org.openide.explorer.view.BeanTreeView.selectionChanged(BeanTreeView.java:146)
   at org.openide.explorer.view.TreeView.callSelectionChanged(TreeView.java:824)
   at org.openide.explorer.view.TreeView$TreePropertyListener.run(TreeView.java:1440)
   at org.openide.util.Mutex$1Exec.run(Mutex.java:1244)
   at org.openide.nodes.Children$ProjectManagerDeadlockDetector.execute(Children.java:1835)
   at org.openide.util.Mutex.postRequest(Mutex.java:1250)
   at org.openide.util.Mutex.postRequest(Mutex.java:1213)
   at org.openide.util.Mutex.postReadRequest(Mutex.java:568)
   at org.openide.explorer.view.TreeView$TreePropertyListener.valueChanged(TreeView.java:1410)
   at javax.swing.tree.DefaultTreeSelectionModel.fireValueChanged(DefaultTreeSelectionModel.java:629)
   at javax.swing.tree.DefaultTreeSelectionModel.notifyPathChange(DefaultTreeSelectionModel.java:1078)
   at javax.swing.tree.DefaultTreeSelectionModel.setSelectionPaths(DefaultTreeSelectionModel.java:287)
   at javax.swing.JTree.setSelectionPaths(JTree.java:1611)
   at javax.swing.JTree.setSelectionRows(JTree.java:1684)
   at javax.swing.JTree.setSelectionRow(JTree.java:1659)
   at org.openide.explorer.view.TreeView$PopupAdapter.showPopup(TreeView.java:1494)
   at org.openide.awt.MouseUtils$PopupMouseAdapter.maybePopup(MouseUtils.java:189)
   at org.openide.awt.MouseUtils$PopupMouseAdapter.mousePressed(MouseUtils.java:180)
   at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:263)
   at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:262)
   at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:262)
   at java.awt.Component.processMouseEvent(Component.java:6264)
   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:4235)
   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)