Spring NamespaceHandler issue when launching Maven-based GWT App from Eclipse IDE after migration to Spring 3
When developing with Maven, you should launch the DevMode from your target/${project.finalName} folder, after a call to mvn package or simply mvn war:exploded (which will copy your dependencies to the WEB-INF/lib there).
See http://code.google.com/eclipse/docs/faq.html#gwt_with_maven and http://code.google.com/p/google-web-toolkit/issues/detail?id=6619
If you have multiple spring dependencies on your classpath, then you may be running into this issue with maven:
To fix this, see the comment from Chris Wilkes. You need to copy the spring.handlers and spring.schemas into your META-INF directory.