When Adobe and OverDrive issue updates for Adobe Digital Editions, the Adobe ID that you registered your computer or device with previously may become de-activated. The way to fix this is to re-activate your Adobe ID on any device on which you plan to read or download an eBook.
First, be sure that you have the most recent version of Adobe Digital Editions downloaded and that you are using the same Adobe account email (your Adobe ID) and password that you originally used. Your e-reader device must be authorized with the same Adobe ID as your computer.
Confirm your original Adobe Digital ID by clicking on the appropriate menu option on your desktop version of Adobe Digital Editions (see below) or reset your Adobe Digital Editions password via the Adobe website. Please note that failure to use the same email and password may make already checked out material inaccessible via that reader.
What to do if there is a 'User Not Activated' or 'Loan token not found' error when trying to read an eBook on a NOOK. This is also helpful for other eReaders. http://help.overdrive.com/customer/portal/articles/1481594
What to do if your NOOK or other eReader is not detected by Adobe Digital Editions http://help.overdrive.com/customer/portal/articles/1481102
Please get back to us if you need assistance with the process for a specific device.
Have a new computer or device?
Whenever you use a new computer for eBooks from an OverDrive-powered site, you will be prompted to 'Authorize' Adobe Digital Editions (ADE). To enjoy eBooks on additional computers or devices, be sure to authorize each one with the same Adobe ID. You may authorize up to 6 devices with the same Adobe ID. For instructions see:
How to Authorize Adobe Digital Editions on a Computer http://help.overdrive.com/customer/portal/articles/1481077
Authorizing a Supported eBook Reader with an Adobe ID http://help.overdrive.com/customer/portal/articles/1481508
How to Clear Authorization Credentials in Adobe Digital Editions http://help.overdrive.com/customer/portal/articles/1481120
For error message "Error Contacting Authentication Server" see http://help.overdrive.com/customer/portal/articles/1481656