I haven't been on XBL for several months with my modded system, but had no trouble in the past.
Recently set up a wireless adapter, and when I run a network test everything is fine until I get to Xbox Live. It tells me I need an Update, and then goes to download the update.
The problem is that as soon as it starts to download, it stops and sends me an error message saying it can't download.
It doesn't even bring me back to the network test page, so I can't see any error codes.