That error looks to be very broad in what could cause the problem. Here are some things you can try:
- Comment out options to see if they trigger it.
- What kind of mouse are you using? The last I checked moused did not support more than seven buttons. This is probably not the cause of the segmentation fault, but it could annoy you later. You can tell X to directly use the mouse. I have to do the same with my Logitech MX1000 by using /dev/ums0 and disabling moused (setting moused_enable and moused_nondefault_enable to "NO" in /etc/rc.conf).
- Test with the nv driver to see if it happens there. If yes, it is less likely to be related to the nvidia/nv driver.
- You may try to asking on firstname.lastname@example.org to see if anyone else has seen problems with the X server unrelated to nvidia drivers. There is also an archive.