1. Just to be clear is the xml you have posted your /WEB-INF/dispatcher-servlet.xml? That is the one causing the problem so make sure the spring mvc namespace is declared there.
2. After you have tried #1, What version of Spring do you have on your classpath? You are specifying 3.0 in your XSD.
3. Are you building your project with Maven
? Make sure you are not pulling in multiple versions of Spring. Try running a mvn dependency:tree from the command line and make sure all the Spring versions look correct and you are not pulling in old versions as transitive dependencies.