Do you mean after too many devices authorized?
Adobe Live Chat: http://www.adobe.com/support/chat/ivrchat.html
They can reset your authorizations, and then you must reauthorize any devices you still need.
(Unfortunately, Adobe haven’t got round to an admin website for viewing and editing authorizations.)
Some of the representatives haven't been properly trained and don't know what to do (and claim there is nothing they can do);
in that case the only way seems to be to give up that chat and try another session hoping for a properly trained representative.
If your problem is with another device using Overdrive, Bluefire, Aldiko or similar third party app, it is recommended not to mention that app when on the chat, just mention that you have run out of authorizations (E_ACT_TOO_MANY_ACTIVATIONS) . Thanks to AJP_Bear for that tip.
I'm having trouble reactivating too but my message says "E_Auth_not_ready"
How long do I have to wait? This has happened several times for no reason that I can figure out. I'll download a library book and then see another one I want to read and then get the error.
Two things that might help with "E_Auth_not_ready" I can't promise either of them will help, but worth a try.
Sometimes ADE gets its registration/activation confused and in a semi-authorized state.
Uninstalling and reinstalling does not help.
Unfortunately, it often then gives misleading error messages about what is wrong.
A common incorrect message informs you that the ID is already in use on another computer and cannot be reused.
This can often be resolved by completely removing any authorization using ctrl-shift-D to the Library screen on ADE (cmd-shift-D if on Mac).
Restart ADE, and then reauthorize with your (old) Adobe ID.
In extreme cases on the mac, the following extra step has helped some people. Navigate to /Users//Library/Application Support/Adobe/Digital Editions and drag the activation.dat file to the trash. If you are using 10.7, see Access hidden user library files | Mac OS 10.7 Lion. http://forums.adobe.com/thread/1265248?tstart=0
There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172