error in compiling build-widgetset.xml

i got this error, um using netbeans 6.9 and vaadin 6.2.3


compile-widgetset:
Compiling com.example.vaadin.countdown into web/VAADIN/widgetsets directory...
Compiling module com.example.vaadin.countdown
   Validating newly compiled units
      [ERROR]
 Errors in 'jar:file:/C:/Users/Mohamad/.netbeans/6.9/libs/vaadin-6.2.3.jar!/com/vaadin/terminal/gwt/client/ApplicationConnection.java'
         [ERROR]
 Line 44: The import com.google.gwt.user.client.impl.HTTPRequestImpl cannot be resolved
         [ERROR]
 Line 493: HTTPRequestImpl cannot be resolved to a type
         [ERROR]
 Line 493: HTTPRequestImpl cannot be resolved to a type
      [ERROR]
 Errors in 'jar:file:/C:/Users/Mohamad/.netbeans/6.9/libs/vaadin-6.2.3.jar!/com/vaadin/terminal/gwt/client/ui/VListSelect.java'
         [ERROR]
 Line 59: The method addItem(String, HasDirection.Direction) is ambiguous for the type TooltipListBox
      [ERROR]
 Errors in 'jar:file:/C:/Users/Mohamad/.netbeans/6.9/libs/vaadin-6.2.3.jar!/com/vaadin/terminal/gwt/client/ui/VNativeSelect.java'
         [ERROR]
 Line 50: The method addItem(String, HasDirection.Direction) is ambiguous for the type TooltipListBox
         [ERROR]
 Line 65: The method insertItem(String, HasDirection.Direction, int) is ambiguous for the type TooltipListBox
   Finding entry point classes
      [ERROR]
 Unable to find type 'com.vaadin.terminal.gwt.client.DefaultWidgetSet'
         [ERROR]
 Hint: Previous compiler errors may have made this type unavailable
         [ERROR]
 Hint: Check the inheritance chain from your module; it may not be inheriting a required module or a module may not be adding its source path entries properly
Java Result: 1

Solved , the problem was in my vaadin version
it was 6.2.3
newer one solved the problem , 6.7.X