I've got the same problem like others discussed before, using MacBookPro (Middle 2014) OS X 10.10.3 AND
Deauthorizing does not work either. So there is no way to get further to authorize ADE again.
I changed to a new MacBookPro, had bevore ADE working on MacBooPro( Middle 2010) under Yosemite. I transfered all datas to the new MacBookPro of course. When I opened on the new book first ADE, it asks for my AppleID, then it showed all my e-Books (gray shaded), but with authorize error, when I tryed to open the books. Therfore I downloaded the newest ? ADE 4.0.3. It came with the same error. An Deinstaller for the ADE or ADE 4.0.3 was not founded. So I put both ADE in the trash. Restartet my MacBookPro. Downloaded the ADE 4.0.3 again an had the same error. I'm using 3 more Adobe products and shut them down, while trying the procedre again and again...
I followed more then 5 times the description for troubleshooting, nothing worked : When you download an e-book, using Adobe Digital Editions 1.7 to 1.7.2, you receive the error "E_ADEPT_INTERNAL."
I tryed method 1 and 2. But no method brought me over 1 or 2 steps, nothing did work. I got totally stuck and there seams to be no way to get ever again to my e-books. I bought a new one, just to see if it'll work. But no way.
Please help and thank's if you can. Would be great... Is ther any troubleshooting hirarchie for ADE 4.0.3., I did not found?
For this problem, you need to deauthorize and authorize ADE again.
1. Go-> Go to folder.
Go to folder dialog will appear.
2. Type ~/Library/Application Support/Adobe/Digital Editions
drag the activation.dat file to the trash.
ADE will be deauthorized now.
Now Authorize ADE again [Help -> Authorize Computer].
Hope this works !!