Bootcamp Bootable USB Drive Could Not Be Created

Hello! So after many long hours of trying to get this to work I have still failed. I am using a Macbook Pro with OS X Yosemite Version 10.10.3 I am trying to use bootcamp with two 4gbs usbs. I installed the Windows support software fine on one usb and trying to install the iso onto the other usb. Will this work? Everytime I have tried to create a windows 8 install disk onto my usb I get this error.

I have tried ejecting the windows iso from my disk utility but nothing has worked. Please help me!