This problem is solved, but I would greatly value any insights or explanations any members of this group could provide.
A user discovered that an old, reliable, DLL failed with a message to provide a system DLL I had not noticed before: svml_dispmd.dll. I checked and found the same problem on 3 machines, but there was no problem on my development machine. So I found the missing dll and loaded it on a test machine, which got rid of the first problem, but this gave rise to an error 193 (Invalid Win 32 application) during the attempt to run LoadLibrary with the original DLL.
After much effort, I pinned the problem down to an integer loop counter variable in a minor subroutine - when I declared it as VOLATILE, the problem was solved.
As far as I know, the only thing different about this DLL in recent years is the fact that it is now built using IVF Composer XE 2013 under Windows 7, whereas it was formally built using IVF 10 under Windows XP. All versions have been Win 32. Why did it fail on other machines but not on my developer's machine?
Many thanks in advance,