plane problem

I am building some terrain in 3ds max 2010. I make that terrain from few planes. I made 3 planes:

-the first one was converted to Editable Poly and then, I pulled several vertices up and down, without adding any modifier. Just pull the vertices up and down. give the plane a name, exported it as a dff, make the col file, the txd file, add these 3 files into gta3.img using ImgTool and add the plane to the game, using MEd. It works!

-the second one was converted to Editable Poly and then, also, I pulled several vertices up and down, without adding any modifier. Just pull the vertices up and down. give the plane a name, exported it as a dff, make the col file, the txd file, add these 3 files into gta3.img using ImgTool and add the plane to the game, using MEd *

-the third one was converted to Editable Poly and then, also, I pulled several vertices up and down, without adding any modifier. Just pull the vertices up and down. give the plane a name, exported it as a dff, make the col file, the txd file, add these 3 files into gta3.img using ImgTool and add the plane to the game, using MEd *

*When opening the game, it crashes. Why? What to do in order to make deformed terrain and why the game crashes, after following the same procedure for making terrain that worked for the first plane?

Please help!!!