Check the USB Drive Body
Checking the USB drive body means you check the unlocked position of some old USB drives that still have this structure. These are mechanical switches; you just switch them to Write Protect USB mode. The switch is quite small and sometimes gets caught on something in your bag or computer case. In this case, you just need to move the switch to the unlocked position and copy the files again.
Now, USBs have modern designs and there are almost no USBs with this switch anymore.