A couple of folks have reported issues to me via my blog about errors downloading television guide data in Media Center 2005 when they install a SonicWALL firewall device on their network.  Our guide download team has debugged this issue on a Media Center system that a Microsoft employee reported this problem on and found the following:

SonicWALL has an option in one of their settings pages (diag.html) which allows you to enable or disable HTTP byte range requests as part of the gateway anti-virus filtering process.  If that setting is turned off (which it is by default on the SonicWALL device we debugged on), then guide downloads will not work within Media Center.

If you have a SonicWALL device on your network and cannot get guide download to work, you can use the following steps to resolve this issue:

1. Navigate to http://<your_router_IP_address>/diag.html from a computer on your network (by default this URL will be http://192.168.168.168/diag.html)
2. Enable the setting to allow HTTP byte range requests in the gateway anti-virus filtering process
3. Reboot the SonicWALL firewall device
4. Attempt to download guide data within Media Center again

The underlying cause for this issue is that the guide download service in Media Center relies on the background intelligent transfer service (BITS) in Windows, and the BITS service requires the ability to request and receive byte ranges to support key scenarios involving data throttling and download restarting.