Cave story won't read a .Prt file

So, I wanted to make my own Prt file but every time I try to get to the area with that specific .Prt file the game gives me an error and I've tried everything I could think of. Even merging it with another .Prt file that I don't use but still it gives me an error.

(The screenshot is of the error it gives me.)

 

If you're wondering, .prt files don't exist. To be more concise...

.pbm files are the tilesets themselves, they contain the graphics data (and are just renamed .bmp image files.) Unless you're using like, CSE2 for your mod, in which it's .png files. Edit those in your favorite sprite/image editor, like paint.net (free) or Aseprite (paid, but open-source).

.prt files don't exist. What DO exist, however, are .pxa files, which contain metadata for tilesets, how each tile behaves. You can edit those directly in Booster's Lab by selecting a .pbm/.png tileset and right clicking the individual tiles.

 

So, do you know what the "1" could stand for in the error message?

 

Nope. Also, edited prior message to be a bit more accurate.

 

The "1" means the the file exists but there was an error loading it, which means that your image editor messed up and the image either
1. isn't a bitmap, it's actually a renamed png or something.
2. it is a bitmap, but it's in a format CS doesn't recognize.
Either way, the solution is to resave the file and/or use a different program to do so. We usually recommend saving images as 24 bit bitmaps since CS understands those, and it lets you use whatever colors you want.

Also, I would recommend deleting error.log after you resave the image(s), just so you don't get confused between old and new error messages.