I have some possible solutions for the person asking about problems with Kobo. I went through this extensively with Kobo last year.
They have to make sure that their Kobo authorization email is exactly the same as the one that are using in Adobe Digital Editions and your Adobe login email address. If that doesn't fix it, then it's possible that the download to your DropBox is considered your legal download and it will not allow you to download your books to another platform.
You also might try to double-click on the epub file that you just downloaded from your DropBox so you can save the file to ADE.
If you get this Steve, it is great to run into you onlineafter all these years and see that you are doing well .