My rig has worked flawlessly (kinesis advantage staple berg) with QMK until today.

I used QMK to change one key in my keymap, compiled and went to flash the firmware with QMK Toolbox on map. I have 28 different .hex files for different keymaps I've done over time. They've all written fine.

When what I compiled today didn't write, I tested prior .hex files and none of them are writing, including the default firmware for the staple berg.

Any help greatly appreciated. Having my primary keyboard go down like this is stressful.
this is what QMK Toolbox is reporting

*** QMK Toolbox 0.0.20 (
Supported bootloaders:
- Atmel/LUFA/QMK DFU via dfu-programmer (
- Caterina (Arduino, Pro Micro) via avrdude (
- Halfkay (Teensy, Ergodox EZ) via Teensy Loader (
- ARM DFU (STM32, Kiibohd) via dfu-util (
- Atmel SAM-BA (Massdrop) via Massdrop Loader (
- BootloadHID (Atmel, PS2AVRGB) via bootloadHID (
Supported ISP flashers:
- USBTiny (AVR Pocket)
- AVRISP (Arduino ISP)
- USBasp (AVR ISP)
*** Halfkay device connected
*** Attempting to flash, please don't remove device
>>> teensy_loader_cli -mmcu=atmega32u4 /Users/eric/Documents/ELKA1.29/kinesis_stapelberg_elka129.hex -v
Teensy Loader, Command Line, Version 2.1
Read "/Users/eric/Documents/ELKA1.29/kinesis_stapelberg_elka129.hex": 17056 bytes, 52.9% usage
Found HalfKay Bootloader
Programming.error writing to Teensy