After experimenting with some Serial communication (which may or may not be relevant), the Arduino IDE throws a “Error opening serial port” error when I try to upload new code to the Arduino or use Serial Monitor. This has happened in both Windows and Linux.
In Linux, after a failed upload I tried disconnecting, then reconnecting the board. It was reassigned to the next open serial port. For example, it starts out as /dev/ttyACM0, then moves to /dev/ttyACM1, and so on.
When plugged in, the “TX” LED lights up, then goes dark. When I try to upload to it, the “TX” LED flickers twice, then nothing.