Conflicting terrain constraints

I get the "Conflicting terrain constraints" when I am trying to delete or add a wall/half-wall, fence ANYWHERE on the lot which I have only ever so slightly used terrain tools on. It was perfectly delete-able/addable before and then suddenly I started to notice glitches in the game on the floors. I reloaded the game and the glitch went away but then a new one emerged, which is that I could no longer add any walls anywhere or delete any walls. I don't think it's because of the terrain tool use, because I only raised the lot slightly in certain areas. Even on the areas that are untouched by terrain tools I cannot build. This is happening in Sulani. Anyone have this happen? How can I fix? 

MM