When nothing else works, you can try reinitializing the flash drive back to the conditions similar to when it was manufactured.

First, you need to determine the file name for the flash drive. Insert the flash drive in a USB port and execute the following Terminal application command.

diskutil list

The file name will be /dev/disk followed by a positive integer. You should also see the phase (external, physical). For example, my 16 GB flash drive produces the output shown below. So the file name is /dev/disk2.

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *15.5 GB    disk2
   1:                 DOS_FAT_32 WINSTALL                15.5 GB    disk2s1

Next, the command to reinitialize the flash drive is given below. If your file name was not /dev/disk2, make the appropriate substitution.

diskutil  partitionDisk  /dev/disk2  1  MBR  FAT32  MYUSB  R

When nothing else works, you can try reinitializing the flash drive back to the conditions similar to when it was manufactured.

First, you need to determine the file name for the flash drive. Insert the flash drive in a USB port and execute the following Terminal application command.

diskutil list

The file name will be /dev/disk followed by a positive integer. You should also see the phrase (external, physical). For example, my 16 GB flash drive produces the output shown below. So the file name is /dev/disk2.

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *15.5 GB    disk2
   1:                 DOS_FAT_32 WINSTALL                15.5 GB    disk2s1

Next, the command to reinitialize the flash drive is given below. If your file name was not /dev/disk2, make the appropriate substitution.

diskutil  partitionDisk  /dev/disk2  1  MBR  FAT32  MYUSB  R