Black Terrain?

[crosscreature]

Hello there! My apologies if there is already a post on this, but I couldn't find it.
Anyways, I have a problem with a map of mine. The terrain textures show up black on the map. To show what I'm talking about, here's some screenshots:

Where the black is, there's supposed to be the texture "green_grass.jpg". But it's not showing up. The texture is one of the default terrain textures that come with the game. And it's like this for any texture I choose (yes, I've tried them all), even terrain texture's I've made.
When I first started this map, I worked on it for about a week straight and everything was perfect. Then, I had to put it aside for a couple weeks because I got busy with real life stuff. I had some free time a couple days ago, so I thought I'd work on it a bit but then ran into this problem. I came back to it today to see if I could fix it, but I couldn't find anything  wrong with the files. I might have missed something though.
If anyone knows what might be happening, please, do tell me. Thank you! ;)

[Enoki]

I'd r'commend checking y'er texture folder f'er the ground texture files. More than likely they are still there, but just in case, ye might as well look.

I would check the terrain mask and see if that's the issue. Upload the default terrain mask to see if the ground textures show up. If they do, check to make sure that ye didn't accidentally rename y'er mask file or typed the name incorrectly. If the name is fine, try editing the mask and re-exporting the file.

[Kynvuu]

As Enoki said, you might want to check that your Terrain Mask is correct. Make sure that your Red, Green, and Blue are the rights shades of RGB. If they are even one number off then it won't work. So that means, for an example, that the blue you used should be:
R: 0
G: 0
B: 255
and etcetera for red and green.
Also make sure your image is in RGB mode as well as all layers are flattened. Hope this helps! c: