I have written about how to make a bootable USB installer for Windows 7 and 8 by using the Windows 7 USB/DVD Download Tool. Sometimes if your USB stick has something in its MBR you might get the error
We were unable to copy your files. Please check your USB device and the selected ISO file and try again.
I found the solution to that problem in this post.
You have to start command prompt as an Administrator (On Windows 7 that means right clicking the cmd and selecting Run as Administrator) and use the diskpart utility.
- Start command prompt as Administrator and type diskpart
- type list disk
- type select disk and number of your USB disk ( like select disk 1 )
- type clean
- type create partition primary
- type select partition 1
- type active
- type format quick fs=fat32
- type assign
- type exit to exit the diskpart utility
- type exit to close command prompt