What I did was deauthorized and reauthorized my ADE, both the device and computer. It worked. I was able to download my books onto my e-reader. Here is a link to what I did Deauthorizing and reauthorizing Adobe Digital Editions 2.0 on your computer and your reader | Washington County Coopera…
I would think that it shouldn't matter if the ADE is 2.0 or 3.0.