From time to time, an error occurs when working with CircuitPython. Here are a variety of errors that can happen, what they mean and how to fix them.

File system issues

If your host computer starts complaining that your CIRCUITPY drive is corrupted or files cannot be overwritten or deleted, then you will have to erase it completely. When CircuitPython restarts it will create a fresh empty CIRCUITPY filesystem.

This often happens on Windows when the CIRCUITPY disk is not safely ejected before being reset by the button or being disconnected from USB. This can also happen on Linux and Mac OSX but it’s less likely.


To erase and re-create CIRCUITPY (for example, to correct a corrupted filesystem), follow one of the procedures below. It’s important to note that any files stored on the CIRCUITPY drive will be erased.

For boards with CIRCUITPY stored on a separate SPI flash chip, such as Feather M0 Express, Metro M0 Express and Circuit Playground Express:

  1. Download the appropriate flash .erase uf2 from the Adafruit_SPIFlash repo.

  2. Double-click the reset button.

  3. Copy the appropriate .uf2 to the xxxBOOT drive.

  4. The on-board NeoPixel will turn blue, indicating the erase has started.

  5. After about 15 seconds, the NexoPixel will start flashing green. If it flashes red, the erase failed.

  6. Double-click again and load the appropriate CircuitPython .uf2.

For boards without SPI flash, such as Feather M0 Proto, Gemma M0 and, Trinket M0:

  1. Download the appropriate erase .uf2 from the Learn repo.

  2. Double-click the reset button.

  3. Copy the appropriate .uf2 to the xxxBOOT drive.

  4. The boot LED will start pulsing again, and the xxxBOOT drive will appear again.

  5. Load the appropriate CircuitPython .uf2.

ValueError: Incompatible .mpy file.

This error occurs when importing a module that is stored as a mpy binary file (rather than a py text file) that was generated by a different version of CircuitPython than the one it’s being loaded into. Most versions are compatible but, rarely they aren’t. In particular, the mpy binary format changed between CircuitPython versions 1.x and 2.x, and will change again between 2.x and 3.x.

So, for instance, if you just upgraded to CircuitPython 2.x from 1.x you’ll need to download a newer version of the library that triggered the error on import. They are all available in the Adafruit bundle and the Community bundle. Make sure to download a version with 2.0.0 or higher in the filename.