"Unable to load DLL ... The specified procedure could not be found" C++ on Windows XP

I have a largish multi-module program that includes a DLL for a C++ program. This worked fine for many years, also on Windows XP. Don't usually test the program on Windows XP, but after a pause of a year or more (during which time lots of things were happing to the non-C++ parts of the program) I did test it, and now it was failing with the exception ""Unable to load DLL ... The specified procedure could not be found - HRESULT 0x8007007F". Tried all sorts of things, and eventually found the solution - see the answer below.

During the period when I hadn't tested on Windows XP I'd upgraded my development system from Visual Studio 2010 to 2012, and hadn't noticed that Microsoft had deprecated C++ support for Windows XP! Fortunately, they "upgraded" (downgraded?) VS 2012 so it supported Windows XP again in "Update 1". But you have to modify the project settings to get it to work.

All of this happened late last year, and I was blissfully unaware of it. :-(

http://blogs.msdn.com/b/vcblog/archive/2012/11/26/visual-studio-2012-update-1-now-available.aspx http://blogs.msdn.com/b/vcblog/archive/2012/10/08/10357555.aspx