[Quickie]

try this one

pawn Код:

public OnPlayerRequestSpawn(playerid)
{
    if(pInfo[playerid][Skin])
    {
        if(pInfo[playerid][Skin]!=GetPlayerSkin(playerid))
        {
            SendClientMessage(playerid,-1,"Skin Locked / You already have a saved skin");
            return 0;
        }
    }
    return 1;
}

EDIT: make sure that his saved skin is not a CJ skin