If Finder displays the "Error Code -50" message when attempting to connect to Air Sharing follow the instructions that can be found at Apple support.
These errors can be resolved by relaunching the Finder.
Double-Check that your iOS Device is on the same wireless network as your computer and that Air Sharing is running on your device. Then try resetting your router by unplugging it for 30 seconds and then plugging it back in. And also try this: