I hope someone can help with this!

Basically, the ground has disappeared from exterior cells when I look at them in the GECK. I'm getting this problem in all of the files - if I look in the base fallout3.esm the same thing applies. Everything is floating in space.

I've got a picture here, part of Seward Square: http://i569.photobucket.com/albums/ss132/JW1a/GECKSeward.jpg

Any idea what's going on? The ground appears to be OK in the game itself, including in cells that I've added to.

Veiw --> Show/Hide window --> Check 'Terrain'. Does that solve it for you?

LOL, I've never noticed that option. Cheers!