A guy said why are the custom skins not working anymore..

Fiction-^ from the Multi Theft Auto forum

MTA Team has forced to block our customized files from gta3.img (IFP, TXD, DFF and many others) to prevent from "cheating" on every server (You can still use custom vehicles on other servers)
You can still play with them by enabling some function in your mtaconfig (Only local, not in other servers)

Really disappointed about blocking our gta3.img it just gave me heart attack when i knew they patched it for totally useless reason
Even more disappointed about they FORCE YOU to UPDATE your client when you try to join a server with an older version, sad as hell

So the other guy answered CodyL anyway from the Multi theft auto forum

Servers can change the config file to allow it, but it is disabled by default.

Soo Drakath i have a question for u, can u ever maybe change the config from ur server to allow the custom skins ? it would be really very nice Dude.