IncompatibleClassChangeError when extending LightIdeaTestCase in 929

Sorry people if this is stupid but i have a test that extends LightIdeaTestCase. I am using EA version 929, and have generics included in the project. The testCase has become very simple -> no constructor is defined (though i have tried with a constructor). When setup() is called, i call super.setUp(); this call never completes but a java.lang.IncompatibleClassChangeError is thrown. I cannot get to the bottom of this, anyone have any ideas? or have come across the same problem and have a solution?
I have checked my classpath, and the idea jars are all the correct version (929), The TestCase is a new TestCase (i.e not converted from extending TestCase) and i have deleted the classes directory for the project, deleted all cache from (entire system directory excluding licence) from .intelliJIdea. I am running windows XP Pro, jdk 1.4.1_05, junit 3.8.1?? I have switched to using the junit.jar in idea/lib - still same runtime error??

Bronwen