Can't book flight despite being available?!

Hi,
I'm trying to book a flight back from LAX to LHR on Weds 25/08/2010 on the Virgin website. It says that the flight is available but when I select it and hit next it says that the flight is no longer available.
I've looked on SeatCounter and there is availability in most classes. Plus, it's available on Expedia.
Does anyone know why I can't book it and whether there's any chance of it 'opening up' for booking at any point? I'm wondering whether to book through Expedia but am worried that the flight has been cancelled but not everyone's been told yet!
Thanks.
I'm trying to book a flight back from LAX to LHR on Weds 25/08/2010 on the Virgin website. It says that the flight is available but when I select it and hit next it says that the flight is no longer available.
I've looked on SeatCounter and there is availability in most classes. Plus, it's available on Expedia.
Does anyone know why I can't book it and whether there's any chance of it 'opening up' for booking at any point? I'm wondering whether to book through Expedia but am worried that the flight has been cancelled but not everyone's been told yet!
Thanks.