I know you had this issue a month ago. Just wanted to tell you I think I know why it fails to save. Are you using a non Microsoft brand usb stick? Because I'm using a Kingston 1gb and I didn't have any problems saving to it. But when I reformatted it from the Xbox, it said it doesn't meet Microsoft performance. I always said yeah okay whatever click a, but when I reformatted it a few days ago that message came up again as it always does. Then it dawned on me it says you might have an issue saving to the usb stick.
So I guess your problem is you were using a non Microsoft usb stick like me and that's why we're having these issues.