Struts2中的Unable to load configuration异常如何解决？

控制台报这样的错误，请哪位大神告诉一下什么原因呢
Unable to load configuration. - interceptor-ref 
      - file:/D:/Java/apache-tomcat-6.0.32/webapps/examquestions/WEB-INF/classes/struts.xml:28:49
	at com.opensymphony.xwork2.config.ConfigurationManager.getConfiguration(ConfigurationManager.java:58)
...
Caused by: Unable to find interceptor class referenced by ref-name excludeParamsStack - interceptor-ref 
      - file:/D:/Java/apache-tomcat-6.0.32/webapps/examquestions/WEB-INF/classes/struts.xml:28:49
	at com.opensymphony.xwork2.config.providers.
      InterceptorBuilder.constructInterceptorReference(InterceptorBuilder.java:52)
...