Try to import a download to my ereader. ADE say: ERROR! check Activation. How can I get my downloaded books to my new Kobo?

Can anybody help me?

I have ADE (4.0) with some books in it.

I became a member of a library and I got a new e-reader KOBO glow.

When I download a book from the library, ADE gives "ERROR! Check Activation".

I do not know what this means and I am not good with computers. Who can help me, please?