I'm developing a website on dfblog (not accessible to pubic yet) and am running into the following issue:
When permalinks are turned on, IE6 and IE7 consistently & occasionally 404 when navigating the site. This does not happen with any other browser -- tested FF, Safari, IE, Camino, across PC & Mac (except no testing on IE8).
Additionally, with permalinks turned on, in IE6, when you navigate away from the root, the div #head and div #wrap seem to lose transparency and become gray/blue.
Turn off permalinks and these problems go away.
Both the CSS & HTML have been validated, and I've made no changes to the theme except add a few pages.
No plugins are installed.
I've just tried installing your most recent build (1.1.5) to a new theme directory with the same results.
I've tested other themes and they are not exhibiting this behavior - it's dfblog specific it seems.
Visiting your blog (http://www.danielfajardo.com/) with IE6 or 7 does not exhibit this behavior.