Let's see the attached usb drive
$ sudo diskutil list
Now, from the list, note the usb drive name and path
$ sudo diskutil eraseDisk FAT32 NAME MBRFormat /dev/diskX
Your usb drive is usable again
Let's see the attached usb drive
$ sudo diskutil list
Now, from the list, note the usb drive name and path
$ sudo diskutil eraseDisk FAT32 NAME MBRFormat /dev/diskX
Your usb drive is usable again