xbase's upgrade path is broken: 4: 0:2.0.0-4.fc4 5: 0:2.0.0-3.fc5 6: 0:2.0.0-3.fc5 The FC-4 one is newer than the others. https://www.redhat.com/archives/fedora-extras-list/2006-May/msg00083.html
Fixed with 2.0.0-5 for FC-4 and FC-5. (plague got a yum error trying to build devel, but I'm trying to get it done as well).