Why am I unable to place any tiles on my map?

The title says it all. I have so far been unable to place a single tile from my tileset on the map. I have a feeling the issue is stemming from the fact that I’m using single pixel tiles. Can I get any direction on this front?

Here’s an image of what I’ve got so far: Imgur: The magic of the Internet

The problem isn’t the 1px size of the tiles, but the fact that you have Terrain Fill mode on, but no valid terrain set selected. Disable this:
and you should have no trouble using your 1px tiles.

Thankyou that worked