I forgot to mention, the intention behind having an 'error node' or 'error process' is for humans to analyze what went wrong and determine what to do for that specific exection thrown for that specific asset that is being modified in the process instance.
just a comment regarding error handling, i am using the same way for handling of errors:
for each node where some kind of error can happen, i make a transition to an "AdminNode" and the admin node has transitions to each of all other node so that via a web interface an "admin" can view all process variables etc, and decide on which transition the workflow should go (or terminate the process completely)
You could define an exception handler and inside the action handler class you can put the token in an arbitrary node in the graph with Token.setNode(Node node). Possibly that node can be a process node...