OPC UA: Calling method Sinumerik

Question

I'm trying to call this method using OPCFoundation library. To select a program

Methods:

NodeId node = new NodeId("ns=2;s=/Methods/Filehandling");
NodeId method = new NodeId("ns=2;s=/Methods/Filehandling/Select");
object[] argument = new object[2];

argument[0] = new NodeId("ns=2;s=Sinumerik/FileSystem/Part Program/EXAMPLE.MPF");
argument[1] = channel;

var result = _session.Call(node, method, argument);

But it's throwing the excepcion:

 BadNodeIdUnknown

And I checked that node exists.

I don't know what nodeId i have to use as objectId argument of Call method.