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 something is 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 on the micro:bit or an error beginning with a 5 on the micro:bit screen, try to flash the same program again. If this doesn't work, please report it to us with the following information:

  • The version of the micro:bit you are using
  • The Operating System and browser (including version) you are using
  • The DETAILS.TXT file from your micro:bit
  • A link to the editor you were using when this occurred  eg
  • The name of any anti-virus software you are running
  • Any accessories you are connecting to the micro:bit and the name of the extension you are using
  • A copy of the .hex file or link to the program that caused the initial problem
  • It is often helpful, but not essential to send a high-quality photo of the front and back of your micro:bit so we can rule out any damage to the components on the board

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