Tomcat Security Manager Weird Error

Hello Everyone,
I have installed tomcat6 on ubuntu 11.10. When I start tomcat with security enabled i get this error:

Caused by: java.lang.RuntimeException: Error building service proxy for service 'RegistryStartup' (at org.apache.tapestry5.ioc.internal.services.Registr yStartup(Logger, List) (at RegistryStartup.java:36) via org.apache.tapestry5.ioc.services.TapestryIOCModul e.bind(ServiceBinder) (at TapestryIOCModule.java:49)): Unable to locate class file for 'java.lang.Runnable' in class loader WebappClassLoader
context:
delegate: false
repositories:
/WEB-INF/classes/
----------> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@4d9 11540
.
at org.apache.tapestry5.ioc.internal.ModuleImpl$4.inv oke(ModuleImpl.java:327)
at org.apache.tapestry5.ioc.internal.OperationTracker Impl.invoke(OperationTrackerImpl.java:74)
... 44 more
Caused by: java.lang.RuntimeException: Unable to locate class file for 'java.lang.Runnable' in class loader WebappClassLoader
context:
delegate: false
repositories:
/WEB-INF/classes/
----------> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@4d9 11540
.
at org.apache.tapestry5.internal.plastic.PlasticInter nalUtils.readBytecodeForClass(PlasticInternalUtils .java:375)


Any idea what permission needs to be granted for this error to be resolved?

Thanks,