I have the same situation, but with a borrowed library book. The librarian chat line indicated this has happened with a number of people today. They suggested de/reauthorizing my computer for Adobe Digital Editions but when I try to do that, it doesn't accept my ID or password. PS Your English is perfect.
The option for authorizing is not available. It's in pale so I can't click on it.
Erasing the autorisation is available, but I tried and it doesn't work ether.
I can enter my email and password, but it refused to erase it.
I must say I'm a bit upset with Adobe customer services... "Talk to each other and find it buy yourself!"
I guess it is not so perfect (my english), but you are very sweet. <3
Finally solved the problem. On your Mac menu bar GO, select Go to Folder, Library, Adobe, Digital Editions. Drag to trash the Activation.dat file. Log into Adobe Digital Editions do command shift D, type in your id and password, select Erase........ It will have you resign in. Hope I'm not missing anything because I was trying all sorts of stuff but this above information fixed it. I've downloaded a book from my local library than copied it into my nook. Hope this helps
Thank you! Worked like a charm. Once I deleted the activation.dat file all I had to do was reauthorize my computer.