Maybe you messed up one of the folders (it's not exactly well organised inside that .rar file)
in the Mod folder, Copy:
-one of the DLLs that are in the folders: "DLL for 126.96.36.199" or "DLL for 188.8.131.52 or later (EFLC too)"
-and the folder Scripts
to the root folder of the game, for example: "C:\Program Files\Rockstar Games\Grand Theft Auto IV\"
Check that first, if you placed it all in the correct maps
Then open up SparkIV and replace the playerped.rpf inside the pc/models/cdimages with that one in the .rar file. I've opened it up myself and all the correct files are in there. But just keep in mind that pretty much every jacket has an a,b and c version and the modder only replaced 1 version of 1 jacket with the ghost rider jacket. So go through the clothing options in the trainer again but also check the various versions.