WP E commerce digital download help

In the WP E-Commerce plugin, I’m creating a digital download. When I try to add the file from “Select from Existing Files” tab (near the bottom) the selection box is completely empty. I thought the “Select from Existing Files” tab would allow me to grab media from my library. Is there a WP E-Commerce tutoral, or digital download tutoral? thanks in advance.

*additional information. I’m not sure if this is related. My book is almost a GIG. To get around the 10mb file upload limit, I added the file to my server (bluehost) and used the server to move the file into my uploads folder. Then I used the plugin called “Add from server” to move the file into my wp library. I CAN see the book in my library, but can’t see any file when try to “Select from Existing Files.”