No flooring on basement/pool

[BoneDigger]

I have 64x64 lot and i cant build basements/pools ONLY on 1st floor under ground (the other floors are ok). Here are screenshoots:

1st floor underground: Notice the pool - it ACTUALLY has floor only on grid, the rest is just glitched floor, i cant place lights, ladders etc. on it


2nd floor

3rd floor



Notice the grid on 1st floor under ground and on 2nd and 3rd.
i dont know how to make that grid on 1st floor underground to be 64x64 and not 40x40 like it is now .
please help.

[Twinmum]

Looking at the first shot and the shaping of the grid, I would say that you have some different ground levels on top. Do you have any ponds, or have you used the CFE cheat at all? These can both affect the ability to add things on the level below. A screenshot of the ground level may be helpful