Yeah, I just recolored an existing tileset, nothing much, I didn't add any colors, only changed them.
Oh, and it doesn't matter that the "event colors" are changed a bit, right? Many tilesets have changed those colors and they work fine...

EDIT: Even when I use an original tileset, unchanged, with set and mask, it gives an error, so I don't think the pictures are the problem...

I have everything on the place JJ2 is installed, so yeah...

EDIT EDIT: It says it cannot open the .bmp file, not find it (if that helps).