* When you download an ebook for the first time, Adobe Digital Editions connects to an activation server.
If the activation server is not available or your network settings don't allow it to connect to the server, you will receive a DRM error.

*If you use Adobe Digital Editions to open or read electronic ebooks on a computer other than the one where you bought the ebook, you will receive a DRM error.

*The system clock has been changed on your computer. The DRM system can track the system clock to prevent users from overrunning the expiry dates of library ebooks and other expired items.

Firewalls, antivirus software or proxies can block Adobe Digital Editions activation via the Adobe server. If you receive this error message your computer can't connect to the activation server http://adeactivate.adobe.com/.

To resolve this problem, change your firewall or other software settings to let your machine to connect to activation server http://adeactivate.adobe.com/.

In Windows XP, add Adobe Digital Editions to the firewall exceptions list:
1. Select Start > Control Panel > Windows Firewall.
2. Select the Exceptions tab.
3. Click on Add a program.
4. From the Add program menu, select Adobe Digital Editions.
5. Click OK.

Carefully check your computer time, date and time zone to be sure that they correspond to the date / time / area where you purchased the PDF or ePub file.
In most cases this will resolve the error.

Open Adobe Digital Editions, press CTRL + SHIFT + D together, quit, then restart the software.

This message indicates you have already downloaded the file on another computer. You have the right to open the ebook on the computer where you download it (or a maximum of 6 other devices authorised with your Adobe ID.)