Every now and then iTunes show a error “16xx” and “21? after a reset or a firmware downgrade. This may also be simply mounted the usage of iREB.
iREB is a software by way of iH8sn0w which can help you fix such errors. So now all you need to do is – when you get such error, run the program and follow the instructions displayed on the screen.
The application is only compatible with EDGE iPhone, iPhone 3G and iPod Touch 1G and can be downloaded