barbapapa

I'm in Win7 professional 32bit, and i've a regular iso of Win 7 32bit and a regular version of Win 7 64bit, and i use USB DVD Download Tool to creata a boot usb pen with Win 7 but if i select en_windows_7_professional_x86_dvdx15-65894 i've no problem, but if i select it_windows_7_professional_x64_dvdx15-65821 it say: "the selected file is not a valid iso file" but... what?? why? thanks for answers