There's a difference between ebooks and physical ones. The copyright laws
(Digital Millenium Copyright Law) restrict how many electronic copies of a
source can be had by one person to combat illegal copying, and I think
you're caught up in that situation. You can check on what properties the
publisher has assigned to the ebook by bringing it up in Library view in
ADE, then clicking in the upper left corner (tiny arrow) to get a drop-down
menu. Then, click on the Item Info tab and you'll see the ebook's
When you download an ebook, ADE assigns rights to it based on the
publisher's properties. It will record the computer on which the ebook was
downloaded in the ebook record. So, if you try to transfer it to another
computer that has ADE, that machine will be able to determine if it's
already registered on another computer, and keep you from accessing it on
the second computer.
Sorry! But I hope this helps.
The book is one that you obtained from the Library, which means there is an extra bit of information ("Loan Record") that is put on your machine when you download the content. To get this to work on a second device you have to do the transfer through ADE which will copy the "Loan Record". However this won't work between computers. To get this to work on a second computer your best bet is to try to redownload it from the website (if possible) or to copy the ".acsm" file which is what starts the process for downloadin with ADE. By doing a redownload, you will get the "Loan Record" onto your second computer.
If you can't redownload, or use a .acsm file, then your next best bet is to download something else from the same library on the second computer.
This was very helpful, and enabled me to copy several books to another computer. The process described here (copying the ".acsm" files from My Documents/Downloads, and then re-downloading), however, is not what is described at Adobe Digital Editions Help, which suggests that we simply need to copy the downloaded files from one computer to the other. It would be beneficial if Adobe were to clarify the process for transferring library books.