嵌入式tomcat下strut2启动报错问题

刚接手strut2，写了个strut2的小例子，在MyEcplise中通过部署Tomcat发布，可以正常启动。但换成嵌入式的Tomcat后，启动就报如下的错：
Unable to load bean: type: class:com.opensymphony.xwork2.ObjectFactory - bean - jar:file:/D:/workspace/Tomcat/./wwwroot/WEB-INF/lib/struts2-core-2.0.11.jar!/struts-default.xml:30:72
at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.register(XmlConfigurationProvider.java:208)
at org.apache.struts2.config.StrutsXmlConfigurationProvider.register(StrutsXmlConfigurationProvider.java:101)
at com.opensymphony.xwork2.config.impl.DefaultConfiguration.reload(DefaultConfiguration.java:131)
at com.opensymphony.xwork2.config.ConfigurationManager.getConfiguration(ConfigurationManager.java:52)
at org.apache.struts2.dispatcher.Dispatcher.init_PreloadConfiguration(Dispatcher.java:395)
at org.apache.struts2.dispatcher.Dispatcher.init(Dispatcher.java:452)
at org.apache.struts2.dispatcher.FilterDispatcher.init(FilterDispatcher.java:201)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:221)
at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:302)
at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:78)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:3666)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4258)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:736)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1014)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
at org.apache.catalina.startup.Embedded.start(Embedded.java:823)
at com.Test.main(Test.java:47)
Caused by: Bean type class com.opensymphony.xwork2.ObjectFactory with the name xwork has already been loaded by bean - jar:file:/D:/workspace/Tomcat/wwwroot/WEB-INF/lib/struts2-core-2.0.11.jar!/struts-default.xml:30:72 - bean - jar:file:/D:/workspace/Tomcat/./wwwroot/WEB-INF/lib/struts2-core-2.0.11.jar!/struts-default.xml:30:72
at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.register(XmlConfigurationProvider.java:193)
... 17 more
2063 [main] ERROR core.StandardContext  - Error filterStart
环境：JDK1.6  
嵌入式的Tomcat：Tomcat/5.5.28