[ 57.836] (EE) Failed to load /usr/lib64/xorg/modules/extensions/libvnc.so: /usr/lib64/xorg/modules/extensions/libvnc.so: undefined symbol: key_is_down I've lost count of how many times this module has been broken by updates. When combined with bug 848943, which was filed almost a year ago but still has not been fixed, the two bugs together frequently render my system inaccessible remotely at exactly the times when I can't do anything about it, i.e., when I'm away from my desktop which is exactly why I need to access it remotely. Can't anything to be done to prevent X server updates from being pushed that break tigervnc, or tigervnc updates from being pushed that are incompatible with the currently available X server?
You haven't included the n-v-r so I can't be sure, but I think you are looking at a test update which has been unpushed. What does 'rpm -q tigervnc' say?
It appears you are correct: yum distro-sync solved the problem.