There is a new beta version of these workshop materials available here: http://ronallo.com/iiif-workshop-new/
The same materials are available there in basically the same order. Please consider trying out that version and reporting any bugs. You can always return here if something doesn't work there.
The suggestion is the make your identifier look something like this:
The identifier for the manifest is usually just the URL that you serve your manifest from. For the purposes of the workshop we're serving up our manifest from http://localhost:3000/manifest.json so we'll use that as the identifier.
Edit your "manifest.json" to look like this: