<?xml version="1.0" encoding="UTF-8"?>  
     <!DOCTYPE dwr PUBLIC  
         "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN"  
         "http://getahead.org/dwr/dwr20.dtd"> 

报错：

Referenced file contains errors (http://www.getahead.ltd.uk/dwr/dwr20.dtd). For more information, right click on the message        in the Problems View and   
        select "Show Details..."  

解决方法：
是因为http://www.getahead.ltd.uk/dwr/dwr20.dtd已经不存在了，改成http://directwebremoting.org/schema/dwr20.dtd即可