That's one of the built-in RPG Maker tilesets so you need to install the RPG Maker VX Ace RTP as the file isn't included with the actual game download.please don't ignore me :,( since the r7, then the r8 and now the r9 update I have had this problem when I want to run the game this message appears, the strange thing is that sometimes it works one out of every 100 times I try and then I close the game and I want to start it again and it appears again, what can i do?