Sigma lens for Nikon, adaptor, and Sony NEX-5R?

So I got a new lens and the adaptor to connect its alpha-mount to my camera s e-mount. My NEX comes up with an error message about not recognizing the lens when I know everything is connected properly. How can I troubleshoot?

Have you read your manual, or contacted the manufacturer's website?

Many of these adapters can't recognise or control aperture, but they should state that explicitly.

If this were a surplus lens from another camera, maybe an adapter would be worth trying. But why in the world buy a wrong-mount lens plus adapter?

You are supposed to buy E mount lenses for full functionality.
Try it in shutter priority mode.

Correct. Your camera does not recognize the lens. Why are you surprised? Shoot in manual mode then. I just hope that lens has an aperture ring.

Next time, stick to the same lens mount system unless you know exactly what you are doing.

Try to return the whole thing. If Sigma does not have the lens in your Sony e-mount, then get it from another vendor.