Bootcamp stop when copying windows files in usb

hi

i just bought a macbook air 13 (2014),when i tried to install windows 7 through bootcamp i had a problem

when copying windows files,bootcamp stoped copying windows files and i waited 2 hours for it to continue copying but it just froze !

here is a photo for the problem in the attachements :

As you can see bootcamp stops there and rfuse to proceed !

help me please

thank you,

Best Regards,