Check activation error message is popped up every time I try open a book.

[janampandya]

I tried using both 3.0 and 4.0 version in my windows 8.1 HP laptop. Doesn't work. What could be the solution?

[thomasi34810468]

I had the same problem after upgrading to Digital Editions 4.0 on Windows 8.1.  I could open books purchased previous to upgrading but not those purchased after upgrading to 4.0.  I resolved this by de-authorizing and then authorizing Digital Editions 4.0.