Suddenly, all 6,000 photos from my iPhone 3Gs have disappeared off the phone. Luckily, I synched the phone into my PC so I think the photos are safe. Now, I want to return the photos to my phone but a message asking for a code to unlock my phone backup keeps appearing. What is this code? How is it set? I don't see any code on my phone except for Passcode lock in the settings.