There are different Class Error messages you will see in Spring, they aren't the same and they add a lot of confusion because they both related to configuration issues, but different types of configuration problems.
1) java.lang.ClassNotFoundException: class is not on the classpath. Add the library using Build>>External Jars.
2) java.lang.NoClassDefFoundError. The JVM went to the classpath and could not load the class from the classpath. It was found, but was defined incorrectly. This usually indicates a problem with the spring xml config files. This is not usually a problem with the classpath.