It would be nice if such a great software like the unetbootin get this little glitch fixed. If you need further input please let me know.
Reading the comments above there are some more who have this problem and it is reproducable at least for me with different kinds of usb sticks. Maybe you can change the "incomplete" status now and start working on the problem. there's an option "-a" for it.), it would be VERY NICE and CUSTOMER-FRIENDLY to - AT LEAST - mention this problem (and the obvious solution) on your website in the documentation. If you don't get it to mark the partition as active (should not be THAT hard: it's just a byte/bit on disk, maybe you could get the code from syslinux source.
* Replug in Computer, try to boot from it -> Tada! It worked just fine! * Plug it in Linux Box, mark partition as bootable (fdisk -> a) * Plug it in Computer, try to boot from it -> did not work. This is a quick walkthrough of creating a G-Parted bootable usb drive. All features of the GParted application can be used. It is also a great platform for performing hardware diagnostics on hard drives. GParted is a free partition manager that enables you to resize, copy, and move partitions without data loss. It works great for resizing, copying, and moving partitions without data loss.
* Under Mac OS X 10.8: started Unetbootin, Installed Centos 6 from ISO to stick: All went fine! GParted (Gnome Partition Editor) is a free graphical partition editor.
* Under Linux: fdisk /dev/sdb -> Primary Partition created, Type W95 FAT32 ("b") (! not marked as active, as this is not required anywhere in your description on unetbootin. * Prerequisite: An already used SANDisk U3 Cruzer 16GB (or any other stick laying around!)