Error: Check Activation - One book only

Hello,

I ordered the DSM-5 as an ebook from appi.org about 6 months ago. It worked for a while until I had to upgrade to Windows 10. I deleted the book because it wouldn't open in Digital Editions, and I figured I needed to redownload it like I had to with my Kindle books. I redownloaded Digital Editions, AND redownloaded the DSM-5. Digital Editions works with the free ebook downloads, but when I successfully download the DSM and try to open it with Digital Editions, I get a messages that says "Error: Check Activation." I called customer service for appi.org. The lady gave me a new digital ebook free of charge, but I had the same problem. I just dished out another $124 to buy ANOTHER ONE, and it still will not open--but the free ebooks from the same website will open just fine in Digital Editions. I even tried to hit "add to library" to scan my files and pull the downloaded ebook in that way, but when I did that, the digital ebook file that is in my download folder (yes, I'm looking in the right place) did not show up.

I looked at the format of the file I'm downloading, and it says "Adobe Content Server Message" so is that not the book at all???

My Digital Editions has authenticated my computer, it isn't asking me to reenter an ID or anything, it's just that one book that will not open, and I need it for class--not to mention my career! I'm a visually impaired student and I can't read a hard copy of the book. I need this fixed ASAP.