Tip: Error occurred in deployment step Activate Features: Object not set to an instance of an object
Yet another SharePoint vagary. If you’re trying to deploy a feature and get the unhelpful error: “Error occurred in deployment step ‘Activate Features': Object not set to an instance of an object” check the scope of the feature that you’re trying to deploy. I added a new feature to a project that had another working feature. Both were calling the Microsoft.Office.Workflow.Feature assembly but only one was failing and it was only after a lot of messing about that it turned out to be this innocuous little setting.