Can't place empty lots in empty custom neighborhood.

I'm not sure how to fix this. I keep trying to place empty lots (with NOTHING) on the in certain parts of the custom neighborhood I downloaded and it won't allow me to do so. There aren't any hood decos like trees, etc. in the way, or other lots for that instance.

Don't know what to do. The plans I have for my hood will be messed up if I can't place them.

I have TS2UC if that's important info..