"ADE could not connect to the server. Make sure you're connected to internet" ???

I Have a PC and downloaded ADE to be able to transfer on my e-reader.

I'm getting this message:

"ADE could not connect to the server. Make sure you're connected to internet", when I want to open a downloaded book from a public Library.

I am connected, I've just downloaded a book from a Library  !!!

I succeeded to open the book on the same ADE ID on my IPhone. Someone told me this could be the problem : the same ID on 2 different machines. But we're supposed to be able to read the same book on any device and restart where we left the last time, whatever device we used !

Someone can explain to me ?

It was working before...Was there an update which scrapped everything ? I've got the latest version of ADE...

I bought an a-reader to use it but I need to download books on my PC to be able to use my e-reader !!!

PLEASE HELP MEEEEEE !!

P.S.: My first language is french, so be indulgent !