Error 5000: No connection could be made

I’ve just updated a Couchbase 3.1 installation (Windows) to the v4 RC. It seems to do the upgrade OK and recognised the pre-existing installation. However, I then go into cbq and any attempt at running a N1QL query gets the following…

ERROR 5000 : Post http://localhost:8093/query: dial tcp 127.0.0.1:8093: ConnectEx tcp: No connection could be made because the target machine actively refused it.

Is there some setup step that I am missing?