I have recently installed IntelliJ IDEA 13.1.4 and the jRebel plugin. I have licensed it ok and created and added configurations in catalina.bat file.
catalina.bat
When
Make sure your class is declared as public and not 'default'
public class MyClassTest
as opposed to:
class MyClassTest
When creating a new test class via IntelliJ shortcut the generated class was not declared as public and that caused the error.