Hi there! Thank you for downloading the pack, and for the support, I really appreciate it. I've just opened the file with the walls and floor, and everything seems to be correct as far as I can tell. The asset sheet should be cut in a 16x16px grid. The sheet have an outer wall with windows, and inner walls and floors which are small tile sets in themselves.
I'm a attaching an example of how the tiles should be cut; so for this example you would use the left and right part of the floor and walls for the sides of a room, and the middle of the wall and floors to fill out inbetween. And then souround all of it with the outer brown wall.
I hope this helps :)