org.apache.bcel.classfile.ClassFormatException: Invalid method signature...

Does anyone have any idea, under what circumstances the following error 
could happen?

Unable to create new instance 
org.apache.bcel.classfile.ClassFormatException: Invalid method 
signature: 
java/lang/Long;Ljava/lang/Long;Lcom/inpoc/srv/parameters/ServiceParameters;)V
        at 
org.apache.bcel.classfile.Utility.typeOfSignature(Utility.java:1024)
        at org.apache.bcel.generic.Type.getType(Type.java:158)
        at org.apache.bcel.generic.Type.getArgumentTypes(Type.java:220)
        at 
org.apache.bcel.classfile.Method.getArgumentTypes(Method.java:226)
        at 
org.apache.avalon.fortress.impl.factory.BCELCodeGenerator.createImplementation(BCELCodeGenerator.java:521)
        at 
org.apache.avalon.fortress.impl.factory.BCELWrapperGenerator.buildWrapper(BCELWrapperGenerator.java:360)
        at 
org.apache.avalon.fortress.impl.factory.BCELWrapperGenerator.createWrapper(BCELWrapperGenerator.java:262)
        at 
org.apache.avalon.fortress.impl.factory.WrapperObjectFactory.newInstance(WrapperObjectFactory.java:94)
        at 
org.apache.avalon.fortress.impl.handler.AbstractComponentHandler.newComponent(AbstractComponentHandler.java:278)
        at 
org.apache.avalon.fortress.impl.handler.ThreadSafeComponentHandler.doPrepare(ThreadSafeComponentHandler.java:72)
        at 
org.apache.avalon.fortress.impl.handler.AbstractComponentHandler.prepareHandler(AbstractComponentHandler.java:179)
        at 
org.apache.avalon.fortress.impl.handler.AbstractComponentHandler.get(AbstractComponentHandler.java:209)
        at 
org.apache.avalon.fortress.impl.handler.LEAwareComponentHandler.get(LEAwareComponentHandler.java:128)
        at 
org.apache.avalon.fortress.impl.lookup.FortressServiceManager.lookup(FortressServiceManager.java:129)

The actual signature should be:
(Lcom/inpoc/srv/messages/RequestMessage;Ljava/lang/Long;Ljava/lang/Long;Lcom/inpoc/srv/parameters/ServiceParameters;)V
And the error is not really 100% reproduceable, sometimes it shows up, 
sometimes not...

Using JDK 1.3.x under Linux for running and JDK 1.4.x under Windows for 
compiling...

Rgds,
Neeme