Error! Check activation

Hi. I download an ebook, but trying to open it with ADE, to transfer to my ereader, I get this error.
I have no clue of computers; contact center doesn't help me, and I'm Dutch and my English isn't too good ... I would very much appreciate if someone could help me step by step 🙂  
It says my laptop is authorized for ADE, so have no clue what i do wrong?