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.