Red box when creating a terrain from curves and points

What can cause terrain creation failure and a red box in place of the terrain ?

Select the Terrain object (the red box) and you’ll see, in the Lands Edit Panel, an Errors tab informing about the problems found and how to solve them,

An usual problem is setting the grid cell size too small, so that the required number of points exceed the maximum defined in the Lands Options. If this is your problem you can just increase this value from the Lands Options dialog (_laOptions command):

You can also increase the cell size instead.