Custom textures in Super Paper Mario

Hello,

I just tried to draw some HD textures for SPM .. The thing is that custom textures won't load in this game ..
I checked "Load custom textures" and set the texture cache accuracy to "Safe" ..
To test if I used a too high resolution for the new textures, I chose one specific texture, not changing anything about the resolution or something, only adding a red point into the middle .. But it won't be loaded ..
Do custom textures not work with this game?