Can't place mine enterance!

[felixdrunk]

So, my friend decided to settle next to a mine, but when he and I try to place the mine enterance, it says you cannot build that their, I shift scrolled to all 8 positions, and it keeps saying that, their is nothing in the way. It is not a well, and looks like an iron mine, any ideas why? I cannot place it on my mine spot either! http://puu.sh/77GX9.jpg
http://puu.sh/77HeJ.jpg

[felixdrunk]

Nvm, we figured it out! You need to pave it depending on the biome!