Comment 4 for bug 139878

vila's solution turned out to work. Both nfs-common and apache2-dev were not getting updated by update-manager, even though they were showing up as needing updates. It didn't occur to me that I would be able to update them via synaptic, because in the past when I have had this problem, it has just created errors. In this case, however, the update in synaptic worked fine, after which the upgrade calculated properly. (I did not actually carry through the upgrade because I didn't have enough disk space, but I did not get stuck at the error "unable to calculate upgrade.")