I have uninstalled and reinstalled It happens on 3 different users on 2 different computers on running Win 7, one running Win 8.1.
This is a software issue. I can't retuen books, I have to wait for the lending period to expire, which means I cannot download any additional books (if I am at my 7 item borrowing limit) until thhe 2 week lending period expires.
What a completely, utterly, pathetically unacceptbale "product." Good way to manage DRM, make your software unusable. At least no one can steal the content.