I`ve got same problem...
Today i emerged tremulous and got same error.
when i unmerged and instaled from binary just this same.
Even downloading backport and running with it displays same error...
Any ideas???
PS. I`ve got same distro:
Sabayon 3.1
kernel 2.6.18-gentoo-r4
X.org 7.1
Nvidia 1.0.9629-r90