No longer able to write to Teensy ++ 2.0

[solo-act]

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 (http://qmk.fm/toolbox)
Supported bootloaders:
- Atmel/LUFA/QMK DFU via dfu-programmer (http://dfu-programmer.github.io/)
- Caterina (Arduino, Pro Micro) via avrdude (http://nongnu.org/avrdude/)
- Halfkay (Teensy, Ergodox EZ) via Teensy Loader (https://pjrc.com/teensy/loader_cli.html)
- ARM DFU (STM32, Kiibohd) via dfu-util (http://dfu-util.sourceforge.net/)
- Atmel SAM-BA (Massdrop) via Massdrop Loader (https://github.com/massdrop/mdloader)
- BootloadHID (Atmel, PS2AVRGB) via bootloadHID (https://www.obdev.at/products/vusb/bootloadhid.html)
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

[PaulStoffregen]

Found HalfKay Bootloader
Programming.error writing to Teensy

This sort of error usually means poor quality USB signals. Circuitry connected to Teensy which draws too much power can also cause trouble.

Try a different USB cable / hub / port / computer. If possible, disconnect Teensy from external circuitry.

[solo-act]

Thanks - turns out with this particular stapelberg teensy, if the error writing occurs and "halfkay connect" with keyboard doesn't fix write error, a simple disconnect/reconnect of the USB cable solves it.

This was how I got around the write error 8 months ago, even with different computer, cables, etc. back then - I just managed to forget. Not sure why that occasional glitch happens, but the solution appears to be repeatable regardless of computer type, cable type and how it's cabled.