My problem was that I chose a 64-bit Ubuntu OS when I signed up with the ISP, Digital Ocean. So I started another Droplet at DO and set it up with an Ubuntu 32-bit system.

All is well now and everything down to the end of sec. 12 in Sven's tutorial works for me. Now I'll look at Deploying For Production.

Many thanks to Sven and Damien for their comments, and to Sven for his fascinating tutorial.

Bruce