Disabling UAC hasn't caused this, I run Poser 6 and 7 on Vista Ultimate 64 and disbled the UAC without issue to either of them!

What "may" have happened is that some of your permissions have changed, you need to make sure you run Poser as an Administartor and also right click your shortcut, go to security tab and make sure you have full permissions on all of Posers folders! 
Vista sometimes lets you access some but not all folders, it really needs setting up properly, it's a PITA from that aspect!

Also what I've found since using Vista is that whenever microsoft send an update down the line, it sometimes resets stuff you've changed which is another PITA!!

I normally include a link to what I think is a reasonably good Vista related site but after the negative comments last time I'm not giving it anymore!

Injustice will be avenged.
Cofiwch Dryweryn.