XBOX 360 Update question

Son has an XBOX 360 when he logs in to it, it says Update available he clicks update now and it comes back with no connection. He is hooked up the following way PC has a wirless connection, cat 5 cable from pc to xbox with ICS set up on pc. The game pays fine online all the time but for the updates he has to take the XBOX system to a friends house who is hooked up similar and plugs his xbox in and it updates, he brings it home and hooks it up and plays on line ok. Checked firewall settings on pc and it is off. When he is on line playing xbox games everything is fine. Only happens when xbox says there is a download available.. Any ideas or pointers., am an IT guy just not a gamer in any way shape or form....

I don't have a 360, but can you download the update from the web to a USB thumbdrive and install from the thumbdrive?

Thanks for the input. Problem is resolved firewall settings on the Linksys