please help. arduino software error.

preferences.txt I edit the file and change it back to default, but still it is an error like this.

java.lang.NullPointerException at processing.app.Base.removeDescendants(Base.java:2296) at processing.app.Base.removeDir(Base.java:2278) at processing.app.Base.removeDescendants(Base.java:2307) at processing.app.Sketch.cleanup(Sketch.java:1224) at processing.app.Sketch.prepare(Sketch.java:1316) at processing.app.Sketch.exportApplet(Sketch.java:1609) at processing.app.Sketch.exportApplet(Sketch.java:1599) at processing.app.Editor$DefaultExportHandler.run(Editor.java:2380) at java.lang.Thread.run(Thread.java:619) Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at processing.app.Base.removeDescendants(Base.java:2296) at processing.app.Base.removeDir(Base.java:2278) at processing.app.Base.removeDescendants(Base.java:2307) at processing.app.Sketch.cleanup(Sketch.java:1224) at processing.app.Editor.internalCloseRunner(Editor.java:1993) at processing.app.Editor.handleRun(Editor.java:1874) at processing.app.EditorToolbar.mousePressed(EditorToolbar.java:324) at java.awt.Component.processMouseEvent(Component.java:6260) at javax.swing.JComponent.processMouseEvent(JComponent.java:3267) at java.awt.Component.processEvent(Component.java:6028) 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(Container.java:4574) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4235) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168) at java.awt.Container.dispatchEventImpl(Container.java:2085) at java.awt.Window.dispatchEventImpl(Window.java:2475) at java.awt.Component.dispatchEvent(Component.java:4460) at java.awt.EventQueue.dispatchEvent(EventQueue.java:599) 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)

Looks like you should re-install Arduino.

thank you for helping. :)