[web2py] Service returns invalid function message

[Matthew]

I have a simple service running in web2py 1.74.6 and 1.77.3. In the
older version, the service works great. In the newer version, the
"invalid function" message is returned. Here is my code:

    from gluon.tools import Service
    service = Service(globals())

    @service.json
    def hello():
        return 'Hello!'

And here is how I call refer to it from the HTML page:

    {{=URL(r=request, f='call/json/hello')}}

Is there a change between how services are called? The documentation
http://web2py.com/book/default/section/9/2?search=services looks the
same.

Thanks,
Matthew