I once had an akmod screw up somehow, and was never able
to figure out how to convince it to rebuild something it
was convinced it already built.
I eventually solved the problem by booting in multi-user
mode, logging in to the console as root, uninstalling
everything named *nvidia*, then reinstalling the nvidia
driver from scratch.
That magically made it work again. Don't know if it
would solve your problem or not, but might be worth
a try (if you haven't already tried it, of course).