If you are trying to install a cooked iPhone IPSW (PwnageTool, etc) and iTunes surprises with error 1600 or 1601 every time you try to Jailbreak your device, do not worry, there is a fix
If you are running iTunes on your Mac, there is a slight possibility that you will eventually run out of luck. I have just successfully Jailbroken my iPhone after having 3 laptops in my room. I had to borrow my brother’s Window Vista to perform this. If you only have Mac for the moment, try those steps first before borrowing a Windows OS.
On Mac OS X
1. Go to ~(Your Username)/ Library/ Itunes/ DeviceSupport/ and delete anything you find in this folder.
2. Go to ~(Your Username)/ Library/ Itunes/ iPhone software updates/ delete all
2. You will likely find nothing in this folder, and the files are very likely hidden, you need to show hidden files by executing a command in terminal, go to Terminal
Copy & Paste in the following order
1.defaults write com.apple.Finder AppleShowAllFiles TRUE (This command will enable show all files in Mac)
2.killall Finder (This command will relaunch Finder)
3. Now you will see some hidden files, go ahead and delete them
4. Go to Pwnage Tool or any other Jailbreak software of your choice and create a new custom firmware
5. Put you iPhone in DFU mode, if you haven’t done so already, and hold Control and point the firmware to the location you saved your custom firmware
If you fail again, Please do not try to switch cables or restart your Mac or any of that crap, it will not work! Instead, borrow someone’s laptop running Windows, and download IREB, you will be fine!
Let me know if you need help in the comments.