You might see a FAIL.TXT appear on your MICROBIT drive when you are flashing a .hex file via USB.


On the latest micro:bit (V2), this will be accompanied by an error displayed on the screen, such as 504


A FAIL.TXT will appear when there is a problem transferring a .hex file from your computer to the micro:bit device. This could be because the file is incorrectly formatted or there is something going on with the computer that is interrupting the transfer, such as anti-virus protection.


The FAIL.TXT will contain the error message and the type


error: The transfer timed out.

type: transient, user 


If you see a FAIL.TXT or an error beginning with a 5 on screen, try to flash the same program again. If this doesn't work, open a support ticket with the following information:

  • The make and model of the device you are using
  • The Operating System and version
  • The DETAILS.TXT file from your micro:bit
  • A link to the editor you were using when this occurred  eg makecode.microbit.org
  • A copy of the .hex file or link to the program that caused the initial problem.
  • The name of any anti-virus software you are running


Please also check that any anti-virus protection you have does not interfere with reading/writing data to USB drives and whether direct flashing from the browser with the apps and editors resolve the issue