ClassFormatError with JDK 1.5

I get the following exception when executing groovysh with JDK 1.5.

C:\Documents and Settings\Clint Combs>java -version
java version "1.5.0-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta-b32c)
Java HotSpot(TM) Client VM (build 1.5.0-beta-b32c, mixed mode)

C:\Documents and Settings\Clint Combs>echo %JAVA_HOME%
C:\Program Files\Java\j2sdk1.5.0

C:\Documents and Settings\Clint Combs>groovysh
[]
Exception in thread "main" java.lang.ClassFormatError: Illegal method name "acce
ss+000"
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:604)
at java.lang.ClassLoader.defineClass(ClassLoader.java:448)
at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:266)
at groovy.lang.MetaClassRegistry.loadClass(MetaClassRegistry.java:122)
at groovy.lang.MetaClass.loadReflectorClass(MetaClass.java:1451)
at groovy.lang.MetaClass.loadReflector(MetaClass.java:1437)
at groovy.lang.MetaClass.generateReflector(MetaClass.java:1390)
at groovy.lang.MetaClass.checkInitialised(MetaClass.java:1343)
at groovy.lang.MetaClassRegistry.checkInitialised(MetaClassRegistry.java
:139)
at groovy.lang.MetaClassRegistry.<init>(MetaClassRegistry.java:84)
at groovy.lang.MetaClassRegistry.<init>(MetaClassRegistry.java:72)
at org.codehaus.groovy.runtime.Invoker.<init>(Invoker.java:83)
at org.codehaus.groovy.runtime.InvokerHelper.<clinit>(InvokerHelper.java
:82)
at groovy.lang.GroovyObjectSupport.<init>(GroovyObjectSupport.java:61)
at groovy.lang.Binding.<init>(Binding.java:62)
at groovy.lang.GroovyShell.<init>(GroovyShell.java:97)
at groovy.ui.InteractiveShell.<init>(InteractiveShell.java:77)
at groovy.ui.InteractiveShell.main(InteractiveShell.java:87)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:494)
at org.codehaus.classworlds.Launcher.launchStandard(Launcher.java:410)
at org.codehaus.classworlds.Launcher.launch(Launcher.java:344)
at org.codehaus.classworlds.Launcher.main(Launcher.java:474)
C:\Documents and Settings\Clint Combs>