Yes i just encountered the floor glitch where you can't place anything after loading a save even though i play as admin.
Anyway in case this happens just go to the campaign select level and load the last save game as many times as you want.
It happened to me like this, i presed resume on main menu i notice the floor glitch by having missing flooring on the 3rd level load save game by going into the campaign and select load or just load a game while being at the level and see if it fixes itself.

Edit: think it's important that you don't save the game when the floor glitched because i think then you are stuck with the glitch in that save file.
At least i just tried what happens if i save game with the glitch and load it then.