Tile loading error when launching

So, I used my own set of tiles to make a small island yesterday, but when I relaunch Tiled to continue, all the tiles that were already placed down look like this

I’m new to Tiled by the way, and I can’t seem to figure out what happened. Any tiles I place down now show up correctly, but the ones that are already there all have that error for some reason. I haven’t changed any file locations or anything.

Hmm, and Tiled does not indicate any referenced files that it can no longer find when you open the map?

If so, can you zip up your files so I can have a look at it?