OK tried all that, still got the fatal error. Tried doing a level 4 uninstall on both printers before repeating the steps in those two documents, still no success. The only thing I was unable to do was temporarily disable services as described in solution two of the error 1603 document - MSCONFIG kept freezing when I clicked on Apply. This time I got a screenshot of the error message from the D1460 installation:
With both printers, the installation gets stuck for quite a while at "Configuring product" before this message appears. The current situation is that the D1460 prints, but when I try to load Solution Centre I get this:
I haven't yet reinstalled the B209a, but I imagine when I do, I'll be back to the same situation as before.