Groovy / Java Mismatch with simple class

The following code compiles and runs as a java class, but yields the error:

java.lang.LinkageError: duplicate class definition: gjdk/groovy/lang/MetaClass_GroovyReflector
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:539)
at groovy.lang.GroovyClassLoader.defineClass(GroovyClassLoader.java:478)
at groovy.lang.MetaClassRegistry$2.run(MetaClassRegistry.java:153)
at java.security.AccessController.doPrivileged(Native Method)
at groovy.lang.MetaClassRegistry.loadClass(MetaClassRegistry.java:151)
at groovy.lang.MetaClass.loadReflectorClass(MetaClass.java:2250)
at groovy.lang.MetaClass.loadReflector(MetaClass.java:2232)
at groovy.lang.MetaClass.generateReflector(MetaClass.java:2182)
at groovy.lang.MetaClass.checkInitialised(MetaClass.java:2129)
at groovy.lang.MetaClassRegistry.getMetaClass(MetaClassRegistry.java:121)
at org.codehaus.groovy.runtime.Invoker.invokeMethod(Invoker.java:142)
at org.codehaus.groovy.runtime.InvokerHelper.invokeMethod(InvokerHelper.java:106)
at c2.invokeMethod(C:\Documents and Settings\Gary Furash\My Documents\Development\StressWebServer\c2.groovy)
at org.codehaus.groovy.runtime.Invoker.invokeMethod(Invoker.java:130)
at org.codehaus.groovy.runtime.InvokerHelper.invokeMethod(InvokerHelper.java:106)
at c2.run(C:\Documents and Settings\Gary Furash\My Documents\Development\StressWebServer\c2.groovy:21)
at java.lang.Thread.run(Thread.java:534)