Unable to open some ebooks on Adobe Digital Editions

I have purchased some ebooks from Google Books and Kobo and they will not open in Adobe Digital Editions. In between buying the first two I bought some more books which opened fine. Since buying the third that wouldn't open, I borrowed books from the library and bought other books from Google Books that opened fine. So over a period of two months I bought about six books and borrowed one and three of those wouldn't open. I have deauthorised and re-authorised my computer but can't think of any other solutions.