I am trying to back up to a USB flash drive. When I go to backup, after about 60 seconds in to it, it tells me to insert a cd or dvd in drive D. I don't know what you call the drive that my usb is in, but it won't backup. I was told by a tech that a usb was a decent backup device. I have windows 7 and use their built in software for backing up. Can anyone help? Thanks.