Why do I get black lines when using a tileset?

Whenever I use the chesthole tileset, I get these strange black lines in between each tile like this:
http://imgur.com/iivhzc7

Does anybody know how to fix it?

That’s grass…yea it looks shit, wait till you see fungus ground.

Those sprites need to be changed cos i can barely tell.

Disable software rendering (graphic option, near the end of the list)