Lately I ran into the tedious "Sealing Violation" when I was trying to debug a J2EE application.
It turned out that I, for some reason, changed the path for the OC4J software. This meant for JDeveloper (10.1.2) to include the JAR files from OC4J and the ones included in JDeveloper. Switching this off makes the "Sealing Violation" go away.