Redhat RHEL 3 & 4 (likely others) for amd64, in at least some common installation pattern, ship without a libX11.so symlinked to a 64bit version of libX11.so.*. This prevents applications that require X from correctly likely. Thus far the only known work around is to all the symlink yourself in the /usr/X11/lib64 dir from libX11.so.6.2 libX11.so.