I bought some extra ATMega 328PUs in the past and also bought an AVRISP mkii to load the boot code. I got it working and did several chips. Recently I bought some 328PUs on Amazon that already had the "UNO" boot loader on them. I figured I would just do the avrdude erase (which I have been doing as a first step anyway) and then load the Nerdkit boot loader on them. It seemed to take the erase command ok, though I'm not sure it does anything to verify. Then I tried to write and it starts writing then tries to validate the first byte. It failed that first byte validation.

Googling yielded too many possibilities on what to do next...I think basically you have to become expert on ATMega boot loading at that point.

So, I'm just wondering if anyone still dialed in to these forum posts has an easy answer.

If you use AVRISP MKII, you can erase the chip and put a bootloader on it, and verify it all by setting the appropriate checkboxes.

If it fails to write, check the comm speed, and make sure it can read the chip identify bytes. If it can't slow the comm rate down. I can communicate using the SPI header at 2MB.

Usually, it's a speed thing and it has to do with capacitive reactance between traces or wires on whatever you're connected to interfering with the signaling.