My D40x is showing an error meassage when I switch the lens to autofocus. It reads; !Error Turn camera off then on again. My autofocus will NOT work with the two lenes I have for my camera,both AF-S. I have used some older lenes with this D40x on manual mode. They are for my Nikon FM. Do you have any ideas for me? Thank you.

I have the same problem and I make this: take out the zoom lens from the body and put it again. The auto-focus comes back. Another my solution: Push autofocus buton to M (manual) and back to A (auto). Then sometimes starts again to work autofocus. But still I know it is not final solution...
Zvonko

Lens motor(inside the lens) could be damaged already. The D40x focusing system is dependent on the lens, just like any other Nikon Dx camera except for the ones that has built-in motor to its body, e.g. D90, D7000. Try a different lens, most likely it should work

Sorry, but the D40x lacks an autofocus motor, depending on the lens to have one. Nikon calls such lenses AF-S. This particular lens does not have such a motor, relying on the camera to have one. The only 50mm lens currently available with an autofocus motor is this one:
http://www.nikonusa.com/Nikon-Products/Product/Camera-Lenses/2180/AF-S-NIKKOR-50mm-f%252F1.4G.html

Earlier this week the Nikon web site listed a new 50mm F1.8 lens with an autofocus motor, but then it was removed. Hopefully they will officially announce this lens soon.

The lens error is due to failure of the lens control system. You can remove battery and card replace battery and while switching on tap the lens hood on your hands so as to disengage any dirt or mechanism being struck.
Use some air to blow between the lens to dislodge any sand particles struck inside. If none of these works then you can think of taking consensus with the service centre.
get estimate before you decide. It will be good to have it checked at the Nikon service as you do not have to run around for spares.

Press shutter button again. If the error doesn't go away, take the camera to the authorized dealer repair shop.

The D40x only autofocuses with the latest AF-S (and old professional AF-I) lenses. Most traditional (screw-type) AF lenses from 1986 through today will not autofocus on the D40x. If your lens says "AF-S," you're fine.
Most lenses sold today for the D40x are AF-S, and so is the included 18-55mm kit lens. Many non-Nikon lenses from Tamron, Tokina, Quantaray, Sigma and anyone other than Nikon still won't autofocus on the D40x. Try before you buy, but honestly, there isn't much the included 18-55mm lens won't do.
Autofocus systems are fast, but not usually instantaneous. You have to hold the shutter down halfway as you compose the first shot so the AF system can focus and lock, and then the camera fires instantaneously when you press the shutter the rest of the way. See Preventing Shutter Delay for more.

All Sigma:
50-500mm f/4-6.3 DG
50-150mm f/2.8 EX DC HSM
70-200mm f/2.8 DG MACRO
80-400mm f/4.5-5.6
100-300mm f/4 DG
120-300mm f/2.8 DG

We tried the same lens on another Nikon (D90) and auto focus did not work.
We mounted a new set of lens on the original D40x, and it worked.
Turns out the 2 year Nikon lens (18mm-135mm) was bad. Nikon lens have a 5 year warrantee. The lens will be sent back to Nikon with no service or shipping charge.

Thanks,
K

Try removing the lens and then reloading it.   Hope this works.

I was having the same problem with my D40... but I read your post, tried switching the 18-55 lens to manual, then back to auto, and it seems to be working fine now. Hmmmm... think maybe there's a circuitry issue with the lens?