I have the
root object error as well - but so far, only for one particular file, that appears to decrypt fine, but then when opening it in Adobe Reader, I get that error. If you try to open the decrypted version in Adobe Digital Editions, you get one blank white page.
I will be changing device soon, so this is why I did this - bizarrely enough the book in question (which I legitimately paid for) is about the President of the USA. Maybe he has better security
All the others have converted absolutely fine - PDF and EPUB.