nvidia 32bit driver

Mon Sep 1 20:59:23 UTC 2008

Hello!

I just install my new FreeBSD7.0 system, everything its up tu date, but when I try to install /usr/ports/x11/nvidia-driver I always got the following error message:

===>  Building for nvidia-driver-173.14.12
===> src (all)
"/usr/share/mk/bsd.kmod.mk", line 12: "can't find kernel source tree"
*** Error code 1

Stop in /usr/ports/x11/nvidia-driver/work/NVIDIA-FreeBSD-x86-173.14.12.
*** Error code 1

Stop in /usr/ports/x11/nvidia-driver.
*** Error code 1

Stop in /usr/ports/x11/nvidia-driver.

Do you have any idea what the problem could be?