"This device isn't eligible for the requested build."

Question

I have an iPhone 3GS with 4.3 firmware. I downloaded a 3.1.3 firmware and was hoping to restore the iPhone using Organizer. But! I got the following error:

"This device isn't eligible for the requested build."

Any idea what's wrong?

Answer 1

There is no officially supported way to downgrade the firmware of an iPhone.

Apple only allows upgrading to a later version.