I am having the same problem and will inform my Public library today. If they are paying a license fee then they are paying for a service that is not rendered. Either Adobe or Apple need to fix this problem.
I tried checking with my Public library and also with the Apple help forum. I was directed to Adobe forums to ask for help. Seems like no one wants to deal with this.
Just got some great advice to delete ADE 4.0 and upload ADE 3.0 .... Did this and problem no longer occurs. I was able to upload and open book from my public library without the error message.
Same problem here. I downloaded and installed ADE 4.0.3 just to check out a library e-book using DRM on my Mac OS X Yosemite. ADE crashed every time I attempted to open that book with a memory address exception. I had no problems opening the default book that comes with the reader though. Looked at iTunes reviews of ADE and Mac users have been complaining about this serious bug since February! What a major fail by Adobe.
I took the suggestion in this thread of downgrading to ADE 3.0. I still had the library's e-book in my library but was now getting a E_ACT_NOT_READY error each time I tried to open it. After some googling, I figured out I needed to reset my authorization token by doing Command-Shift-D. But after regenerating my authorization token, I got a E_LIC_ALREADY_FULFILLED_BY_ANOTHER_USER error. Now I think I need to get the library to reset the authorization token for the book since my token has changed. I dropped them a note informing them Adobe Digital Editions 4.0.3 doesn't work on Yosemite and asked them to reset the authorization. I've removed the book from my ADE library and will hopefully be able to download and start reading it next week.