That's why closing the app each time helps - because it delays things just enough for the crucial license step to take place. My working theory is that the new machine is too fast - that if ADE is already open when I try to fulfill the next book, it happens so quickly that some necessary step with the license for the EPUB file has not taken place yet. Still, it's annoying to have to exit from ADE every single time, and then wait while it starts up again, every single time I want to download a Libby EPUB book. The several-second delay while ADE started up seemed to be all that was needed for the EPUB file to be fulfilled. I finally figured out a workaround, which was to exit from ADE after each download, so that for each subsequent download, ADE had to start up again. Then it got worse, and even multiple refreshes of the page did not help. Now and then, I had to refresh the Libby download page two, or even more times, in order for ADE to successfully fulfill the EPUB file.

If I refreshed the book download page, everything would work normally, just the way it used to. License server Communication Problem: FILE_DOESNOT_EXIST' - but only if ADE was already open (for example, if this was the SECOND book I was trying to download). On the new machine, I noticed that with the exact same procedure described above, ADE would often return the error 'Unable to download. Then I recently got a newer, much faster Windows 11 machine. Firefox then automatically opens the ACSM file, which launches Adobe Digital Editions (ADE, currently Version 4.5), which then fulfills the EPUB book file. Once I check out the book, I select the EPUB format and the web browser (Firefox several recent versions over the past year, running under Windows 10) downloads the ACSM file. I've been using the Libby app to download library books in EPUB format for over a year, with no problems.

Libby app on pc