I copied jboss-aop-jdk50.jar and jboss-aspect-library-jdk50.jar from <jboss_home>/server/default/deploy/jboss-aop-jdk50.deployer and made them available to my unit tests. Now it works fine.
Are these jars needed by client applications when running jdk5.0? If so perhaps they should go into the <jboss_home>/client directory?
So i've got the same problem in the past.
The problem is due to the lack of some class in classpath of your client.
So you have to add to your class path the jar file present in