In order to fix error "E_AUTH_FAILED http://adeactivate.adobe.com/adept/SignInDirect" do following.
Open Internet Explorer
In menu bar go to Tools>>Internet Options
Select Security tab.
Now select Trusted Sites.
Click on Sites button.
Now add http://adeactivate.adobe.com
1) Open Adobe Digital Editions.
2) Press Ctrl+Shift+D key of your Keyboard and deauthorize Digital Editions
3) Move your e-books to some different Location.
4) uninstall Adobe Digital Editions from your computer.
Click start>>Control Panel>>Add or remove Program
Select Adobe Digital Editions from the list and Delete.
5) Also delete following files.
Type "regedit" without quotes in the box and hit enter.
Locate the following key "HKEY_CURRENT_USER>Software>Adobe>Digital Editions"
delete the full folder (Right click on it and click delete).
Also locate HKEY_CURRENT_USER>Software>Adobe>Adept
Delete the full folder.
6) Now download and install Adobe Digital Editions from the link given below.
7) When asked to authorize computer then please enter same Adobe ID and password which you were using earlier.
I hope this will help you .!!!