Okay, I have an iPhone 3GS that was jailbroken and unlocked on 4.0.1. I've been trying to update it to 4.3.1. First, I updated it to 4.1 to get the iPad baseband. Then, I built a custom firmware with pwnagetool for 4.3.1. So, I tried flashing it in DFU mode and it gave me error 1600. How do I fix it? I've tried googling for it but a lot of the results were for older versions.