I searched the forums and sites high and low, but couldn't turn up a satisfactory solution to this problem. Tried reformatting several times -- with
fdisk-- all to no avail. Tried reinstalling with
usb-creator. Tried various ISOs.
Ultimately, what did the trick was to delete the partition using
fdisk. Apparently, the partitions on the USB flash disk weren't properly set. I don't know how it happened. Deleting all the partition on the flash disk with
fdiskdid the trick.
Then, next step was to recreate the partition on the USB flash disk, but this time using
gpartedto do it.
A subsequent check using
fdiskshowed that the partitioning problem had gone away.
usb-creatorone more time, and it all worked.