Looks some pretty obscure reasons from a quick web search.
Can you give more details, please?
What have you done with ADE that already works?
What were you trying to do when it failed?
I am actually attempting to assist a customer who is having this issue.
This is directly from their email sent to me:
Operating System: Windows
Description: I am trying to help Tracy McKeel install and download her e-books. When she is trying to activate Adobe Digital Reader with her Adobe ID, she is getting an Activation Server Error. (Code:E_adept_xml_syntax http://activate.adobe.com/adept/activationserviceinfo). I don't know how proceed without getting this error.
I believe she means to say Adobe Digital Editions 2.0, not Reader.
I can make three standard suggestions that often help in obscure cases like this.
I can't promise anything from them, though.
Unfortunately, when it doesn't go right first time it is rather a hit and miss affair installing ADE and getting it running.
Try uninstalling and reinstall;ing ADE 2.0/2.0.1
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
I'll certainly give these suggestions a try. I sincerely appreciate your help with this. Thank you.
I encountered this issue on windows 10 when I tried to Activate Adobe Digital Editions with my AdobeID, but it was solved by closing and opening again the application.