I had added the method to an outer objectNode by a hasComponent references, although I did this after the MethodNode has been constructed completely, i.e. after I added the arguments to the method node.
Before:
1) create plainMethodNode
2) add arguments to method
3) add MethodNode to outer object (hasComponent)

After changing the order of activities to
1) create plainMethodNode
2) add MethodNode to outer object
3) add arguments to method (hasComponent)
the exception is no longer thrown.

While this solves the problem, I find the order a bit counter-intuitive, because, as you quoted Object Oriented Programming, my expectation was rather to first construct the methodNode with all its subNodes and only then add the method to its owning object.

Maybe a little hint could be added to the JavaDoc for the PlainMethod node, explaining the correct sequence.

Anyhow, many thanks for your support.

Best,
Hans-Uwe

This is the version which threw an exception:

PlainMethod uploadMethod = new PlainMethod(serverNodeManager, new NodeId(ns, “uploadConfiguration”), new QualifiedName(ns, “uploadConfiguration”), new LocalizedText(“uploadConfiguration”));
Argument inputArgument = new Argument(“csvConfigurationString”, Identifiers.ByteString, ValueRanks.Scalar, (UnsignedInteger[]) null, new LocalizedText(“Modbus Configuration in CSV Format”));
uploadMethod.setInputArguments(new Argument[]{inputArgument});
configurationObjectNode.addComponent(uploadMethod);

the configurationObjectNode (BaseObjectTypeNode) has been defined earlier in the code

I’m working with the SDK 2.2.0, by the way