Lib log4j conflict


I work on Webmethods 6.5 developper
I have a problem with the log4j library : log4j-1.2.15.jar. I use it in java services and when i put it in the

code/jars folder of my package I can’t launch any service. This error is raised :

java.lang.reflect.InvocationTargetException: ExceptionInInitializerError

When I put the jar in the lib/jars folder of the IS, I have no more errors and all my services work well. I can’t understand why this problem occurs and I need a solution to keep the jar in my package without put it in the lib/jars of the IS.