Elite C Firmware Issue

Hey all, working on a Corne Choc, and having issues flashing the right half of the board with QMK Toolbox.

I am getting a validating error with:

822 invalid byte in program region, 0 outside region

This is the second controller as I had the same error on the first and assumed I ruined it when I was troubleshooting it and desoldering.

Ordered a new board and same issue.

I've cleared the EEPROM, there are not shorts or bad solder on the headers. This is a completely separate PCB.

Tried using QMK MSYS to reflash ISP (not sure I got that right, don't really understand it).

Get a blue led indicating power, reset button works to put it into bootloader mode, still nothing will flash on it.

Unfortunately on the first go round I had soldered headers to swap but was too tall for me, desoldered the boards and went directly to the PCB, as mentioned this is a new board on a new PCB, did not program prior to soldering.