Copy fresh set of CS 2.1 SP2 web files, hook up site in IIS, amend web.config, load Firefox, hit Return, hold breath. Error. But of course. ASP.NET is complaining about an unrecognised section in web.config, which reminded me I hadn't updated the ASP.NET script mappings for that site to ASP.NET 2.0, which was swiftly rectified by running aspnet_regiis.exe (with -s flag). Then also ran the ASP.NET schema update script, as I'd neglected to do that earlier. Hit F5 and... "Object not found...