If these are reskins, you need to match both the file name and the type specified in the texture.txt file, otherwise, this won't work.
Sometimes you can change the file-type and update the texture.txt file to match, meaning edit the text file in you text editor such as notepad and change the .jpg to .tga if you've created .tga files instead.
If you create .tga files, do not save them as compressed files so uncheck the RLE compression option.