问题描述：
An internal error occurred during: "Loading descriptor for cmbc_wms.".
java.lang.NullPointerException
An internal error occurred during: "Loading descriptor for cmbc_wms.".
java.net.UnknownHostException: java.sun.com
原因：
The problem is not the taglib at all, it's just a bad error description by Eclipse.it is the project facet vs. web.xml dtd.. their versions must match!if the web.xml says:<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">but the project has a "Dynamic Web Module 2.5"then this error will occur.. change facet to 2.3 or web.xml to 2.5... in other words: they must match..
web.xml 里如下内容可能不匹配
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"