Okay so I got a 3GS off of Craigslist for my girlfriend. It was jailbroken, activated, and unlocked, but running way back on 4.0. Everything working - tested it extensively. Now my girlfriend erased all content and settings so now it's stuck on Apple logo. Read up, saw that the latest untethered JB is on 6.1.2 so I decided to work with that instead of the latest 6.1.3. So I downloaded a stock build, built a custom IPSW via Sn0wbreeze (used her computer, I'm on a Mac), and made sure to check the bootrom (it was on the new one). Then I ran TinyUmbrella on my Mac, set the hosts to check back to Cydia, and tried restoring to my custom build. No dice. Getting error 1600. Tried multiple computers and multiple USB cables (all original) and multiple ports, still error 1600. Any help?