It got worse.
I uninstalled Quicken 2004, re-installed Quicken 2000 and tried to open the data file. Quicken validated the data, and then refused to open it. Apparently Q2000 cannot read Q2004 data files. Ha!
Off to Microsoft, where there is a free trial of Microsoft Money. (I originally picked Quicken because, back in 1999, Money had no concept of Standing Orders or Direct Debits. How Americans put up with their banks is a mystery.) A surprisingly similar 30Mb later, and “Guess What?” Money can open Q2004 data files. Not perfect, but close enough. And Standing Orders/Direct Debits are now handled. Only £22 including postage from eBuyer.
Intuit, to their credit (-:, offer a 90 day refund. They had come across my problem, and the solution is to upgrade to Quicken Investor (for another £11). I don’t want investment help, I only have some old Bradford & Bingley shares in the Quicken data. I suggested that a better upgrade path might have been to allow me to open my file but just discard the shares.