I tried a couple of days ago with blackra1n but also got stuck in DFU mode. I also tried to put the iPhone manually in DFU mode and restore via iTunes from my custom FW but i received the 16xx error.
I don`t know what to do
Thanks anyway!!!

Hey. I posted yesterday a comment but didn`t got any answer, can anyone help:
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"Hello, I have an iPhone 3GS 16GB white, FirmWare 3.1.2, baseband 5.11, unlocked from factory, OS: MAC OSX Snow Leopard 10.6.1, I just want to jailbreak my iPhone. I tried with PwnageTool 3.1.4 with a custom firmware (also 3.1.2 - custom made with PwnageTool 3.1.4), everything was ok but at the final restart of the iPhone it got stuck in DFU mode (black screen), so i had to restore the original 3.1.2 firmware and now my iPhone is like it was when I bought it. Any suggestions? Thanks!"
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Hello, I have an iPhone 3GS 16GB white, FirmWare 3.1.2, baseband 5.11, unlocked from factory, OS: MAC OSX Snow Leopard 10.6.1, I just want to jailbreak my iPhone. I tried with PwnageTool 3.1.4 with a custom firmware (also 3.1.2 - custom made with PwnageTool 3.1.4), everything was ok but at the final restart of the iPhone it got stuck in DFU mode (black screen), so i had to restore the original 3.1.2 firmware and now my iPhone is like it was when I bought it. Any suggestions? Thanks!