Just a quick update:
I have figured out the problem and it is a weird one. Katsunami actually pointed me in the right direction.
I tried de and then re-authorizing my computer (I didn't know I could do this). This prompted the software to ask for my Kobo login again (even though it had been logged in previously). So I entered the information. Next, it asked for my Adobe login info. So I entered that in as well. But that is where it failed (Just with an error box that said: failed. No more info than that). I tried multiple times but it kept on failing. That was weird because I have had an Adobe login since the dawn of time (I do a lot of work using their products) and I
know my login by heart.
So I went over to the Adobe website to log in there. The very first thing that happened after I logged in (using my correct username and password) is that Adobe forced me to change my password.
And that is when I had my AHA! moment. Adobe had that ridiculous security breach a while back where their entire user base had their login credentials stolen. I never log into my adobe account and my password that I use for their forums was a throw-away password anyway, so I never bothered "fixing" my login.
But they had frozen my account (or something similar) until I created a new password. So the Sony reader desktop app was trying to authorize the DRM on an account that existed but whose password had been partially rejected. Once I reset my password I was able to log into my reader app using the new password and am able to download my books (or at least one of them so far... I am cautiously optimistic about the others).
So, problem solved (I think) and thanks to everyone here for their help.
That said, I want to reiterate that I still think Kobo failed miserably here. Had they had some sort of live chat or phone number that I could have used to contact them directly then all of this could have been figured out relatively quickly. But they didn't and, as such, I wound up almost not being able to read my books while traveling. The root
cause of the problems were lousy programming practices (cryptic error messages such as "failed" or "could not download content" are
stunningly bad programming practices on an consumer facing piece of software), but the
actual problem is that Kobo does not have a decent help mechanism when technical issues do arise. Until such time as they can demonstrate that their help system will not leave you stranded for days and days and days, I would still recommend that people avoid Kobo devices or devices that rely on the Kobo back end.
That said, I am writing (a thoughtful, not vitriolic

) letter to Kobo to try to let them know how I think they could improve their help system. Most likely it will fall on deaf ears, but maybe they will be able to make some changes to improve their customer experience.