Thanks for the reply.
Yes, I checked and both authorizations - ADE and Kobo - mention the same email. We connect both devices to the same computer but I'm assuming that can't be the problem, right?
I'm thinking that it's a firmware issue, since it's the only difference between the devices. I really have no idea why my brother's Kobo didn't updated to the firmware I have, since they were bought at the same store (Fnac) just at different times - might be that he hasn't opened the Kobo software in quite some time?
By the way, I tried using Calibre to upload one the books I had in ADE and had the same result - black cover and when I used the navigate icon, it froze.
This is very annoying!