Canon EF-S lens 18-55mm autofocus issue, Err-99, troubleshooting help please!?

You need to clean the contacts between the camera and the lens. Your camera is having trouble controlling the lens which is why it cannot focus, or stop down the aperature. If that does not work, take it to a professional. They might be able to fix it. I had that problem. Cleaning it good with alcohol worked for me.