The groovy-all-1.0-beta-10.jar contains the ASM library. Normally the ASM library package name is modified when embedded to prevent name collisions with other libraries that use it. Apparently this wasn't done with groovy-all-1.0-beta-10.jar. It is done with more recent versions of the Groovy library (e.g., the latest, groovy-all-1.0-RC-01.jar). The lack of name change can cause problems since the latest ASM's API is different from the one embedded in groovy-all-1.0-beta-10.jar. I would suggest replacing the use of groovy-all-1.0-beta-10.jar with a version with modified ASM package name to prevent problems with ASM name collisions.