Finally! I got my my current Ayumi theme template to validate as XHTML again. This was a bit tough until I found that there was an extra </span> tag in one of the templates. I deleted it and got things working again.
I plan to make some changes to this theme in the future. I need a more organized layout for my static pages. The new WordPress widgits will certainly help here.
Oh, looks like I will need to update to WordPress 2.6.1 as well. Arghh, so many updates. Rumor is that with WordPress 2.7, all of these updates can be down from the Admin panel. That will be nice. 🙂