I haven't been on Xbox Live for a while. When I logged in I was prompted for an update. The update errored out so I hunted around and found the instructions for using a USB drive. I downloaded the update to a USB drive and installed it as per the instructions. Everything appeared to install as explained. When I tried to connect to Xbox Live i get the message that "a system update is required to sign in...but the update is currently unavailable...." I've checked the forum. I've double-checked the instructions, but I have had no luck. What do I need to do?