perche ricevo questo errore quando provo a cambiare la JLabel??

label.setText("nuovo testo");

java.lang.NoSuchMethodError: Threadsecondario: method <init>(Ljava/lang/StringV not found
at sleepwindows.spegni(sleepwindows.java:93)
at sleepwindows.actionPerformed(sleepwindows.java:109 )
at javax.swing.AbstractButton.fireActionPerformed(Abs tractButton.java:1786)
at javax.swing.AbstractButton$ForwardActionEvents.act ionPerformed(AbstractButton.java:1839)
at javax.swing.DefaultButtonModel.fireActionPerformed (DefaultButtonModel.java:420)
at javax.swing.DefaultButtonModel.setPressed(DefaultB uttonModel.java:258)
at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(BasicButtonListener.java:245)
at java.awt.Component.processMouseEvent(Component.jav a:5100)
at java.awt.Component.processEvent(Component.java:489 7)
at java.awt.Container.processEvent(Container.java:156 9)
at java.awt.Component.dispatchEventImpl(Component.jav a:3615)
at java.awt.Container.dispatchEventImpl(Container.jav a:1627)
at java.awt.Component.dispatchEvent(Component.java:34 77)
at java.awt.LightweightDispatcher.retargetMouseEvent( Container.java:3483)
at java.awt.LightweightDispatcher.processMouseEvent(C ontainer.java:3198)
at java.awt.LightweightDispatcher.dispatchEvent(Conta iner.java:3128)
at java.awt.Container.dispatchEventImpl(Container.jav a:1613)
at java.awt.Window.dispatchEventImpl(Window.java:1606 )
at java.awt.Component.dispatchEvent(Component.java:34 77)
at java.awt.EventQueue.dispatchEvent(EventQueue.java: 456)
at java.awt.EventDispatchThread.pumpOneEventForHierar chy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:145)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:137)
at java.awt.EventDispatchThread.run(EventDispatchThre ad.java:100)