Updating to F26 using dnf system-upgrade - conflicts

> [asinha@cs-as14aho-2-herts-ac-uk  ~]$ sudo dnf system-upgrade download --releasever=26                                                                                                                                                         Failed to synchronize cache for repo 'rpmfusion-nonfree-updates', disabling. Failed to synchronize cache for repo 'rpmfusion-free-updates', disabling. Last metadata expiration check: 0:00:18 ago on Wed Apr  5 11:59:31 2017. Error: nothing provides nss(x86-64) >= 3.29.3 needed by java-1.8.0-openjdk-headless-1:1.8.0.121-10.b14.fc26.x86_64. nothing provides nss >= 3.29.3 needed by firefox-52.0-7.fc26.x86_64. problem with installed package lz4-1.7.5-1.fc25.i686. nothing provides nss(x86-32) >= 3.29.3 needed by java-1.8.0-openjdk-headless-1:1.8.0.121-10.b14.fc26.i686. nothing provides nss(x86-64) >= 3.29.3 needed by java-1.8.0-openjdk-headless-1:1.8.0.121-10.b14.fc26.x86_64 (try to add '--allowerasing' to command line to replace conflicting packages)