I have just realised that I no longer have the DX10 preview mode in my display settings. I have the latest nvidia beta driver installed. Any ideas? Thanks in advance.My directX version, according to the dx diagnostic tool, is directX11

Sorry, I found the problem by google search which bought me back to this forum. FOUND IT! I now know what the problem was. I decided to work backwards and uninstall every 3rd party addon or driver one-by-one, restarting and opening FSX Acceleration each time. I discovered the problem is a 3D driver I installed for ColorCode. This allows you to use brown/blue glasses to fly FSX in 3D. It is great stuff and I recommend it. I used their iZ3D version 1.10 Beta 3 driver from here:http://www.iz3d.com/t-dcdriver.aspxFor some reason (does anyone know?) this removed the DirectX 10 Preview check box in FSX Acceleration. When I removed the driver and restarted the check box was back again.Phew! At least now I know.I just have to make a choice between DX10 or 3D, until a suitable ColorCode driver comes along.