Comment 44 for bug 1294877

I can confirm that the bug exists (and has a simple workaround).
Mine is an updated UbuntuMate (15.04) and while trying to create a new Bootable USB pen drive got the same error. As mentioned elsewhere, opened up the pen drive in fdisk, removed all partitions, created one partition as 'c' type (VFAT ...), exit, mkfs.vfat /dev/sdb1. Now when I go back and create the bootable USB it works as expected.

My machine:
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 15.04
Release: 15.04
Codename: vivid