I get an error message when I attempt to download an epub from the library. I have Windowns 8.1 and Digital Editions 3.0

Launch ADE

MAKE sure you are in library view [where you can see all the books listed]

Press "ctrl+shift+d" for Windows or "Cmd+shift+d" for Mac

Deauthorization dialog will come up.

once ADE is deauthorized,

Now again AUTHORIZE ADE

Help-> authorize computer.

Hope this works !!

checked back on the forum.  One advised deauthorising your computer - I opened ADE then hit control/shift and d and the screen will come up to deauthorise.  Deauthorised then  reauthorised the computer and it worked.  Good luck with yours!

Me too!!