What does this web.xml error mean?

Answer 1

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">