I ended up coming across this issue in Refinery CMS after switching databases.

I had forgotten that I had swapped out databases because I had moved on to changing some other configuration bits in following the RailsCast for Refinery CMS.

Fortunately, I found note on Refinery’s Getting Started page that deals with this:

If you get a 404 error on the homepage, try running the rake db:seed and then restarting the server.