You need to make sure your portable electronic Book is registered with the same AdobeID as your computer.
If it is fully compatible with ADE then ADE should ask you to register the device when ADE is run with the device plugged in.
If not, there may be some other way to arrange authorization; tell us which eReader device you have.
There are quite a few devices which ADE 2.0 is having problems with, but which worked on the older v1.7.2.
Version 1.7.2 is a little difficult to find,
available on Adobe site for Windows and for Mac.
Thank you very much for your kind reply and suggestion!
My eReader is Iriver, which I have found in the list supported by ADE. I have registered my eReader. I have tried to download ADE 1.7.2, still blank.
The strange thing is when I open my book with my PC, it can be open smoothly. But when I open it through ADE in my PC, it's blank. That is to say I didn't use my device, I open it in my computer with ADE, it's blank. I was so confused about it. Oh, my god! What's happened to my book????
looking forward to hearing from you for good way to solve this problem!
Is the Iriver behaving properly with non-DRM books?
Try getting one from Project Gutenberg or other free source,
and copying it to the eReader using File Manager (so Digital Editions is not used at all).
Is this happening will all books loaded via ADE?
I found a small number of library books that read ok using ADE on my PC, but could not be read on my Bookeen Opus eReader.
A couple just wouldn't open, one would even crash the Opus when I tried to open it. I can't remember if any opened but showed blank pages.
Almost all the books can be read just fine on the Opus.