webwork 中 external-ref 和interceptor-ref 共同用出现问题

<interceptor name="upload" class="com.opensymphony.webwork.interceptor.FileUploadInterceptor"/>

<interceptor-stack name="uploadStack">

<interceptor-ref name="defaultStack"/>

<interceptor-ref name="upload"/>

</interceptor-stack>

但在aciton中如果单独用external-ref 或interceptor-ref 运行程序时都不出错，但两个合在一起就出错。

<action class="com.chinabankpay.action.ManagerAction" name="addbacktender" method="addbacktender">

<external-ref name="managerservice">managerservice</external-ref>

<result name="success">listbacktender.htms</result>

<result name="error" type="chain">

<param name="actionName">error</param>

</result>

<interceptor-ref name="uploadStack"/>

</action>