No errors or warnings on xhtml or css on those pages, I've checked several times.
I checked DocType again, looks fine.
The strange thing is, I'm certain I checked both of these pages not long ago when I first put them online. I normally check everything with IE and Firefox, as those two browsers represent the majority of visitors to my site. They had to have been OK when published, or I would have fixed them at that point, so I'm wondering if there's another Microsoft update in the mean time that's gone awry.