I'm guessing the Logos web folks already know about this, but just in case... I'm seeing a fair number of missing sample pages when I click links to them on various product pages. As an example:
http://www.logos.com/product/7654/hermeneutics-and-interpretation-bundle
Click the sample pages for The Hermeneutical Spiral book. You end up with the default IIS 7 "404 Not Found" page.
I recommend paying close attention to the IIS web logs for 404 errors to help catch these.
Donnie