ERROR: could not retrieve device serial number. Can't continue.

[wow-hello]

Hello! I am trying to downgrade my iPhone3,1 from iOS 7.1.2 to 5.1.1 (jailbroken), but I keep getting the error: "could not retrieve device serial number. Can't continue." iTunes also shows up with "Serial Number: n/a" when in DFU mode. Does anyone know how I could fix this or even possibly get around it? Please let me know!

Device: 2010 MacBook I got for $50 on eBay
OS: macOS High Sierra 10.13.6
Processor: 2.4 GHz Intel Core 2 Duo
RAM: 2 GB 1067 MHz DDR3
Graphics: NVIDIA GeForce 320M 256 MB