To cut a very long story very short, I have fixed the searchable results page which has been broken for months! Apologies for the interruption.
I use to keep the results in a separate Access database file that I could upload to the web server easily after the race, but the mechanism for reading this broke when my web hosts migrated onto 64-bit Windows Server 2012. On that operating system it is only possible to have either 32-bit or 64-bit Access database drivers, and it wasn't working out well for me. I have now moved this data into the main SQL Server database that runs the web site, and made some minor code changes on the results page to accommodate this. The procedures on race day will change - we will still enter all the results into our standalone race management database, but then instead of uploading the whole file, I'll push some data from that database into the web-facing database over ODBC.
Actually I'm very happy with this - the results page seems to load and query quite fast, and overall it's a better way to do things.