Calibre doesn't render these files correctly. It opens up, for a split second the first page is rendered, then the left half of the background of the first page disappears, so I get a thin white rectangle with text that runs off of it, and then no other pages render.
I think the books I'm working with...they're similar in format to cookbooks or textbooks? A lot of pictures, diagrams, graphical elements, with text set over them, this sort of thing:

Probably needs to be a PDF?