Was running 4.0 on my iPhone4 and decided to upgrade to 4.2.1. Jailbroke with green poison and had no problems. When in safari or my photo album if I double tapped or tried to copy it would crash and bring me back to the home screen. Restored twice and had the same problem. Using tiny umbrella I downgraded back to 4.0. Now itunes is giving me a message that says "can't sync with old firmware, need to update" or something like that. What do I do to get it to sync with 4.0?