You can not build that there

I'm trying to build a house but when I go to place it down it comes up with an error message saying, "You can not build that there." I thought this was because the ground was not flat enough, then I found completely flat land but it still came up with the same message.
Then, I decided just to make sure; I tried to build on somebody elses already planned out land, but it still came up with the same message.

I've even tried using the default client but it still did not work.
Then, I decided just to make sure; I tried to build on somebody elses already planned out land, but it still came up with the same message.
I've even tried using the default client but it still did not work.