The tileset you attached in your original post is NOT formatted as a tileset for use in Ace - it looks like a parallax tileset, because tilesets in Ace must not have any free/transparent space between the tiles. You'll need GIMP or Photoshop to turn that picture into a correct tileset for use in the editor.
Second, there is not one, but six different tilesheet formats for Ace. If you go to the resource manager and view the tilesets there (or go into the help file), you'll see that a sheet for A1 has a different structure than a sheet for A2, A3, A4, A5 or one of the B to E sheets.
Usually Tilesheet names contain one of those combination (A#) in their name to indicate into which slot they go - placing a tilesheet in the wrong slot will cause a lot of problems and make it unusable.