This is the backtrace from Xorg.0.log.old:
Backtrace:
[ 16518.617] 0: /usr/bin/Xorg (xorg_backtrace+0x37) [0x81c29a7]
[ 16518.617] 1: /usr/bin/Xorg (0x8048000+0x17e3aa) [0x81c63aa]
[ 16518.617] 2: (vdso) (__kernel_rt_sigreturn+0x0) [0x4001d40c]
[ 16518.617] Segmentation fault at address (nil)
[ 16518.617]
Fatal server error:
[ 16518.617] Caught signal 11 (Segmentation fault). Server aborting
Best,
Nico