I'm having the same problem.
VGA isn’t always the easiest option. I have a Hitachi 42" TV (42PD8600) and because of its unusual panel dimensions it makes it hard to find the correct settings in the AV wizard as most of them give a similar "Invalid format" message.
If you want to use VGA you have to boot up with VGA connected, go through the wizard and choose your correct connector then reboot, swap cables, and hope you got the settings right. If not and you get the same "Invalid format" message, so its swap to VGA boot up again and try another. But then not all of the settings will output an image with VGA, some of them will be out of the Panels range. I'm aware that I have an awkward TV, but I think VGA for first run of the AVwizard isn’t always the way to go.
I was going to try this tonight but I think I may go with kyfalcons method instead.
Unless anyone can point out something I am missing?