I had this problem and tried all of those things. What finally worked was:
Deleted Open Office
Deleted Digital Editions
Downloaded Open Office
Downloaded Digital Editions and reauthorized
This finally worked
The problem is with the iOS app on iPad, not on my computer. I am able to open the eBooks on my computer already.
Oh, sorry. Try "read on device" instead of using ADE
Or will the books open in iBooks?
Also there is a new app for iPad & iPhone called Libby
Finally, if you can't get books to open directly on your iPad, you should be able to transfer them from ADE on your computer by connecting your iPad to your computer. This is how I get books on my Nook reader
No, I have to use the Adobe Digital Editions app in order to read on the iPad since the books are linked to Adobe account, so those solutions will not work.
Same problem here on iPhone iOS 11.2. I am able to read on surface tablet, see the book (grayed out, Unknown Author) next to the one that comes with the ADE app. But get connection error. Searched other forums without help, obviously re-installed etc but no joy.
Exactly the same problem here... does Adobe have a way to download DRM PDF files (e.g., checked out of my library) onto ADE running on an iPad? Sure doesn't look like it! I'd like to hear a response from them.
Like the original post, I also receive the "Connection Error Detected" error message.
Yes, I am connected to the Internet... that's how ADE got the information from my library.
Yes, the "fulfillment server" is working... I can follow the same process with ADE on a Windows PC and successfully get the book.
No, I cannot transfer the book (using methods suggested elsewhere) by opening another application and "Export"; ADE is not one of the applications in the Export list (groan).
No, I cannot transfer the book using iTunes; iTunes transfers Audio Books, not e-books.
Sorry I don't have a solution for this one and I'm beginning to suspect that a solution will not exist until Adobe decides to fix the application and sent out an update. I guess I'll go back to OverDrive until Adobe gets their act together...