Does anyone know why my Xbox prints "invalid signal" on my TV screen when I insert the Sega GT Online disc...?

I don't have an internet connection, I just want to play offline (it says you can do this on the back of the SGO case).

Thanks.

I am not sure that this will be a help, but I ran into a similar problem with another SEGA title: Gun Valkyrie.  For some reason the game thinks it can run in something besides 480i, but it cannot.  You might ensure that all of the HD video options (480p, 720p, 1080i) are disabled on your Xbox Dashboard.  Worth a try at least, eh?

FWIW, I suspect that it is your TV that is displaying the "Invalid Signal", and not the Xbox.

Hope this helps!
VK