adobe digital editions hangs up during the downloading process

a few days ago my adobe digital editions started hanging up during the downloading process. the download starts and apparently also ends but instead of opening the ebook the programm hangs up and doesn't react anymore so that i have to end it via "force quit". i already tried to de- and reinstall but nothing works. any suggestions? i'd really appreciate it!

i have a mac book pro, osx yosemite, and adobe digital editions 4.5. until a few days ago the programme worked perfectly!