If the micro:bit runs out of resources or detects a fault, it enters a 'panic' routine which displays a sad face on the micro:bit screen followed by a number eg 020.
There are a list of errors on the microbit.org website with descriptions of what they mean and what you can do to fix. In all cases, pressing the reset button on the back of the micro:bit will restart the program, which clears out the RAM memory and starts again.
If your error isn't listed here and you are using MakeCode, there are some additional unusual error codes listed in the documentation
If you are using one of the standard languages such as MakeCode or MicroPython, you would not often see these error messages. If you do, please report them to us so we can investigate.
If you are using C++, then these errors are more likely if you have a bug in your C++ program.
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