Arduino Pro Mini upload error

Other Hardware 3rd Party Boards
2

It may not be anything you did wrong. I can think of 2 possibilities (there could be more, of course)

  1. Your bootloader has been overwritten. To fix you will need to put a new bootloader onto it.

  2. Someone put an optiboot bootloader onto it. The optiboot will not respond to the same up-load protocol as the older bootloaders. Try changing the board type to Arduino UNO or Arduino Mini w/ATmega328.