The only thing I can actually reccomend is that you double check that the trail texture is named correctly. If you are sure it is, and it still doesnt work, try temporarily renaming the trail texture as soemthign else, then taking another texture in your custom folder, copying it and renaming the copy as the trail texture, is this still doesnt work, i think there must be somethign up ith you toribash. If the new trail does show, go back to the texture you want as the trail texture and save as again as the name you want, making sure all layers are corerectly merged and that the image is uncompressed when you save it.