I have exactly the same problem on my HP Envy with Win 8.1. I did successfully download books several months ago, but now nothing. Adobe support chat line couldn't help. They said to go to Overdrive support. HOW? I can't find any way to contact them.
Update: Success! After downloading the small 1kb file from the public library using Overdrive, I went into my download files, double clicked on the file to open it, and selected to open with Digital Editions instead of Overdrive--and there was the full book. I used the Digital Editions page to select my Nook under "computer devices" on the left side of the screen and copied it over. No problem. Hope this helps others and I hope it continues to work on my next download.
Have the same thing with my Sony PRS-350. No problems on old PC with Windows XP but now I have a new PC with Win 8.1 I'm getting the error message. Any suggestions appreciated.
I have gotten the same message from downloading an ebook onto Overdrive and I click to process it and it says "an error occurred when decrypting Adobe EPUB content"
Sorry I don't have a solution!