I was unable to create live USB drive using
dd command while
unetbootin works. The former method used to work fine on the particular USB Drive. Is the USB drive filesystem corrupted? If yes, how do I fix it?
filesystem : FAT 32
Ubuntu isos are not designed to be dd'd to a drive. Use unetbootin or some other tool.
If you want to boot an ISO file in an easy fashion you normally use a tool like unetbootin or others availiable at the http://www.pendrivelinux.com/ web site.
If you want to boot just ISO files specifically you could set up grub2 on a flash drive and use the 'boot iso feature' of grub2. The issue with this method is each disrto seems to have its own special options that must be used to boot properly.
A benifit of this is once you get ubuntu working on it. you can then upgrade the flash by copying over a new iso file. or add several different ubuntu releases by just duplicating the proper grub.cfg lines.
I created a single 8gb flash drive this way that can boot xubuntu, lubuntu, kubuntu, and ubuntu. I am not sure if the persistent save file feature can work using this method.
I have several guides on grub2 iso booting bookmarked at http://www.delicious.com/dr_willis/grub2
If you used dd, it's likely corrupted. To format it: open a terminal and watch the messages while you plug it in.
What was the device name? I'll use sdb for illustration.