What does this web.xml error mean?

I suggest you add ; between 2 passages: xsi:schemaLocation="http://java.sun.com/xml/ns/javaee and http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

Like this:

:xsi:schemaLocation="http://java.sun.com/xml/ns/javaee;http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

replace

xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_5.xsd">

with

xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee;http://java.sun.com/xml/ns/j2ee/web-app_2_5.xsd">

The solution is that you have to put semicolon between URLs

I am sure you will not get the error again :)

If you replace j2ee by javaee, it will work fine.

EDIT :

<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">

Edit:

To know anything further related to this error. Please follow the Link. Here you will find schemas for Java EE deployment descriptors (web.xml).