Actually, though I didn't mention it, the problems I reported were under Vista RC-2.
I have now tested under Vista RTM and I don't the same problem.
I can now create a Nero Digital MP4 file with Recode under Vista RTM that plays back OK under Vista RTM. When I tried it under WinXP it gave the Error -2002 at first but strangely, when I tried it again later it also played OK under WinXP. !!