Which log is this from? Since X is mentioned, be sure check the /var/log/Xorg.0.log file, if you haven't read that one. Errors have `(EE)' at the start of the lines; warnings start with (WW).
I found this error mentioned in an ArchLinux forum: https://bbs.archlinux.org/viewtopic.php?id=77590
This might be a fix:
This is an issue with Xorg, specifically with the new option AccelMethod. Just remove or comment out the following line in your /etc/X11/xorg.conf file and the problem goes away:
However, the error message in your forum title is very general, mentioning the handler and "Fatal X error". If you find an particular error in the Xorg.0.log, it might make a search on Google more accurate.