I am following the http://wiki.alfresco.com/wiki/WorkflowAdministration step-by-step guide to creating a custom workflow.
The anwser to my question, regarding how to get / where to place a new custom-workflow-context.xml file got answered in this very usefull forum topic – https://forums.alfresco.com/en/viewtopic.php?f=30&t=35459
I am once again a little frustrated with the Alfresco system.
Why? The “hello world” workflow won’t work… The simplest.xml workflow didn’t work.
And “A system error happened during the operation: null” is not really a good error in my humble opinion.