To summarize: “checksum error” means that the data Etcher reads from the device is not exactly the same as the one in the disk image that was written.
It may have 2 explanations:
- the SD card or USB drive being flashed is broken and does not write (or read back) the data it is asked to write;
- something writes to the drive between the moment Etcher writes the image and re-reads it from the drive.
The second point seems to be happening frequently to Windows users who flash images containing partitions that windows can read (FAT mostly).
To avoid it, you should follow the instructions here https://superuser.com/questions/1199823/how-to-prevent-creation-of-system-volume-information-folder-in-windows-10-for/1199824#1199824 .
If it still happens, try flashing the same drive from another computer (Linux or macOS preferably). If you still get a checksum error, your drive is not working correctly, if it doesn’t, it means that something on the first computer is writing to the drive before it is done being verified.
In that case, you can flash a drive on the first (problematic) computer, flash the same image to another drive on another (non problematic) computer and compare the files in it using meld for example (on the non problematic computer).