Referenced file contains errors (http://JAVA.sun.com/xml/ns/j2ee/web-app_2_5.xsd).

Referenced file contains errors (http://JAVA.sun.com/xml/ns/j2ee/web-app_2_5.xsd). For more information, right click on the message in the Problems View and select "Show Details..." 

1  其中，若有j2ee一定改为javaee

2  必须是5行（很傻瓜，对于检错却很实用）

3 实在不行，新建一个Web Project，将其中的web.xml拷贝过来

如下：

<web-app version="2.5" 
xmlns="http://java.sun.com/xml/ns/javaee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">