Yes I always install both versions. I can't imagine why it would be your codec pack to be honest as I've been using it for years and its always been superb!
I just loaded each one up as admin and it said resetting to default settings or something similar, then I ticked your suggested settings.
EDIT: For some reason I got it into my head that this was about a another problem I had.
This one unfortunately still remains and its driving me round the bend
I'm beginning to think that its to do with my new fx card, as I've never this with my ATI card.
Come to think about it.... i have a new motherboard....... im stumped