Is this just for one eBook? Do others download OK?
I haven't seen this bug on ADE2.0 before, but general advice ...
There are lots of bugs in ADE2.0. 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 had the same error, deleted Adobe 3.0 from control panel (windows) and reinstalled. Works fine now! Try using a different browser to download it too, like chrome.