The following DRL fails to compile, with error "Syntax error on token "enum", Identifier expected."

package com.sample

import com.sample.DroolsTest.Message;

//The "enum" sub-package causes the problem, not "Enum" class
import org.apache.commons.lang.enum.Enum

rule "Hello World"
when
m : Message( status == Message.HELLO, myMessage : message )
then
System.out.println( myMessage );
m.setMessage( "Goodbye cruel world" );
m.setStatus( Message.GOODBYE );
update( m );
end

rule "GoodBye"
when
Message( status == Message.GOODBYE, myMessage : message )
then
System.out.println( myMessage );
end