Why unable to open the item? Or ”Protected by Digital Rights Management”.

I read ebooks with Adobe Reader. But lately some books (file type epub) are impossible to open. When trying on my PC (Windows 😎 I get the answer ”Unable to open the item. Please contact Sony customer support. Error: document.”. And when trying on my ebook reader Sony PRS-T2 i get the answer ”Protected by Digital Rights Management”.

Moreover, it is the same thing with my android devices (tablet Sony Xperia Z2 and smartphone Sony Xperia ZR), where I use UB Reader to read. My tablet says ”Filformatet stöds inte.” (= The file format is not supported.) And my smartphone says ”Du har inte rätt att öppna den här boken. Kontrollera ditt Adobe ID.” (= You are not allowed to open this book. Check your Adobe ID,)

I have been able to read the ebooks earlier but some months ago (or earlier, I don´t know exactly) this happened. I have a valid Adobe ID and have bought and downloaded the books from big and established book shops.

Do somebody know what has happened? And what I can do, to be able to read the books?