When I import DNG photographs from my camera's SD card to lightroom, the images are banded with contrasting colors. When I import the same photographs into iPhoto there is no banding? What I am I doing wrong?
This is almost always a hardware malfunction of some sort. It could be card reader, USB cable or USB port, hard disk or even memory. You need to try to troubleshoot the transfer process by using different hardware or even an entirely different computer to see if one piece of hardware or another is causing the problem.