I have had the same problem for about a month now. I even tried reverting back to an older version of Digital Editions and it's happening there too. Adobe Digital Editions has never been great software. Before this problem started, it would constantly freeze after I imported .acsm files and I'd have to force close it through the task manager. And now this. I can no longer check out books from the library because I have no way to read them. OverDrive needs to make a few software options available to read ebooks. If Adobe had some competition, they might start giving a damn about the quality of their software and provide some kind of support. Anybody with a monopoly is inevitably going to get complacent, which they've clearly done. As it is, the software feels and looks obsolete and is poorly maintained. It's like a relic from 2010 shoved in a corner with the label "Good Enough" slapped on. Adobe should be embarrassed to have their name on it.
The fix in that thread was what I needed to solve this problem.
It's frustrating. Apparently the problem has to do with an incompatibility between ADE 1.7 and ADE 2.0, 3.0, 3.5, 4.0 or 4.5. And is that ADE does not allow changing the directory "My Digital Editions" and hence the conflict.
In my case, solve it by uninstalling both versions (1.7 and 4.5), delete the folder "My Digital Editions" (of course saving the information of the books). Then modify the 1.7 installer by changing the string "My Digital Editions" to "My_Digital_Editions" (with underscores). Use a HEX editor.
Then reinstall both programs in the following order:
1. ADE 1.7
2. ADE 4.5
Copy the backups into the appropriate folder (with or without underscores). And ready. You have both versions working.
I had the same frustrating problem! How I fixed it was to rename my digital editions folder and move it to another drive then I deleted all instances of My Digital Editions folders on drive C of which there were three. I then ran the installer for version 4.5.6 and it completed and recreated a new digital editions folder and magically populated it with the last 20 or so books that I had borrowed. The program now opens and closes again without error and books can be returned once more.
During the problem period which lasted for 3 weeks I had to install 4.5.6 each time I wanted to borrow a book in order for the download to occur. In this state there was never any visible bookshelf and the program would not close on its own.
I sincerely hope that this works for others out there!
Thanks very much as this has also worked for me.