well, I had the same problem,
I just couldn't find out why it occured or how to fix it by installing or uninstalling codecs.
so I figured out some other solution: I would redesign it with "windows movie maker" as upsidedown again (this time true way).
when I imported it to the wmm, I saw that it was just fine? stupid or what?
then I only saved it as .wma, and that is it.
(yes it became .wma, but nothing else to do. as nero simply solves the problem as burning to cd [as vcd or dvd], no format matters to me)