whaa, you compile your own kernel or it is unstable repository kernel compiled with gcc 4.6?
Because nVidia driver as a kernel module needs to be compiled with this same version of compiler as a kernel.
That's my kernel and I need to change GCC to 4.4 every time when I compile nVidia driver:
:~$ cat /proc/version
Linux version 2.6.39-2-amd64 (Debian 2.6.39-3) (firstname.lastname@example.org) (gcc version 4.4.6 (Debian 4.4.6-6) ) #1 SMP Tue Jul 5 02:51:22 UTC 2011