I suggest that you install and use mkusb, which can restore the USB drive to a standard storage drive (with an MSDOS partition table and a partition with the FAT32 file system). See these links
mkUSB-quick-start-manual.pdf
help.ubuntu.com/community/mkusb
mkusb version 12 alias mkusb-dus:
Often the problem is some data that is 'tricking' the software to think that the pendrive does not work, even when it is good, and it is enough to wipe the first megabyte to get rid of that data. I think this is the case with your drive. You 'look at' the drive with a tool, that does not recognize or understand correctly the structure of the boot system, which was cloned from the iso file.
There are many ways that a USB pendrive can fail. So it is worth trying different things. If mkusb fails, try in another USB port, in another computer and with another operating system. But there is a limit, when you have to accept that the pendrive is probably damaged beyond repair, at least with tools available to normal users like you and me. See this link
Pendrive lifetime
But if there are valuable data in the drive, you should think differently and use special methods to restore/repair the file system or even recover the data without any file system. See this link,
Repair the partition table and file system of a pendrive
fdisk -l
?