Please Help with struts2

[Konstantyn Harasevich]

 Hello

 When running samples struts 2

 Here is exception relative to this taglib in NetBeans7.1:
 <%@ taglib uri="http://www.opensymphony.com/sitemesh/decorator"; 
prefix="decorator" %>







org.apache.jasper.JasperException: /WEB-INF/decorators/main.jsp(26,72) PWC6188: 
The absolute uri: http://www.opensymphony.com/sitemesh/page cannot be resolved 
in either web.xml or the jar files deployed with this application



 Do not now reason why this error appear because this is valid url ?

 Thanks.