To reply to both:
I did try that, and it highlighted a couple of Creative startups that I'd hoped were long gone (now disabled), but little else that I wasn't expecting.
The best clue was:
Fred wrote:One type of application known to interfere in this way is programs that configure your standard mouse such as the MouseImp program.
I have installed a program called Soluto (actually quite useful), one part of which is focussed on minimising boot-up times by removing or delaying startup items. I'd delayed 3dconnexion startup, as I never need to use 3d immediately on bootup, but I do use WizMouse to enable windows focus to follow where the mouse points and rely on it operating straight away.
So, I guessed it was that running before 3dx that was fouling up s80trans.dll
To save (quite a lot of) my time, I mainly put the PC into sleep after each day, rather than rebooting - so I've only just done a full reboot - and the dll load error didn't come up - so it looks like that was the problem.
a final bit:
I do try & put a fair amount of detail in my questions so as to not waste people's time, so the suggestion to check whether the dll file was 'present on the filesystem' was disappointing, as I'd already said I'd checked the dll file was there. And no, there were no un-english words in the filepath - I'd certainly have mentioned that if there had been!