Lens errors are fairly common. Usually it's sand or grit interfering with the lens extension mechanism. Or the camera's been dropped with the lens extended. Or the camera has been powered on, but the lens had been blocked preventing its extension.

I have written a blog post about some things that you can do to try to correct it. They only seem to work for about 50% of lens errors, but they're worth a try. The list includes:

1. Remove the batteries and wait a few minutes
2. Try pressing and holding the Menu, Function, Function Set, or OK while turning on the camera, or otherwise find a "factory reset" option.
3. Try turning the camera on without a memory card inserted
4. Place the camera flat on its back and turn it on while holding down the autofocus button, to try to cause the camera to attempt autofocus while the lens is extending
5. Blow compressed air in any gaps around the lens — or use a shop vac
6. Use a thin piece of paper or a needle to dislodge any visible bits of grit
7. Gently tap the camera in an attempt to realign jammed mechanics or dislodge particles (obvious warning: could cause further damage)
8. Gently push or pull the lens barrel, as a last resort (again, potential for further damage).

The blog post goes into more detail on these ideas.