I got a similar error of "f/0" after putting my 55-300mm lens on my D7000.
I examines the small connecting needles at the rear end of the lens. The number of these needle heads varies depending on the type of lens — a 55-300 has 8 needle heads; a 18-200mm has 10. These serve as connectors from the lens to the camera body. They spring up and down upon installation/uninstallation of the lens to the body. In time, they accumulate dust and do not spring back up. Upon examination of my lens, I found that one of the needles did not spring up when I changed my lens.
I took a household needle and carefully and gently picked up on the sunken needle head while using a hand-air-blower to clean away the accumulated dust. After some patience, the needle head popped again to its normal position, as with the other needles beside it — and the f/0 error is gone and I was able to use my lens again. Please remember to cover the exposed glass at the rear end of the lens while pumping the air blower, so that dust won't move in your lens.
I hope this DIY experience will help. If it fails, I suggest you send your lens to the service center.