I recently had the same error and was able to fix it. so hopefully this could be useful to you
First: check dxdiag (if you're using Windows 7, click the start button and type in dxdiag in the little search bar) - on the second tab, near the bottom of the window are 3 'Direct-X functions'. All of these have to be enabled for GW to work
For me, 2 of the 3 were disabled and I wasnt able to turn them on again (even though the option should have been in that dxdiag window)
If you can't turn them back on in that window - check if you have the latest drivers for your graphics card (install the latest if you havn't and hope that turns those options back on) - Personally I didn't do this step at first, but maybe that wouldve fixed it aswell. I knew I didnt have the latest driver for my gfx card (the latest was the one Nvidia released for BF3)
Personally, I did a system restore to 2 days earlier and that turned those options back on again, and GW started up normally.
In those 2 days I had installed the Battlefield 3 beta, which kept whining about having to update my video driver (even though the game ran fine), my guess is that that game messed up my gfx drivers somehow.
Last edited by Lukyboy; Oct 10, 2011 at 12:18 PM // 12:18..