Sorry,rosszul csináltam.
Helyesen:
[pawn]
new kulcsok[MAX_PLAYERS];
public OnPlayerEnterVehicle(playerid, vehicleid, ispassenger)
{
        if(kulcsok[playerid] == 0)
        {
        new Float:x,Float:y,Float:z;
        GetPlayerPos(playerid,x,y,z);
        SetPlayerPos(playerid,x,y,z+3);
   SendClientMessage(playerid,0xFFFFFFAA,\"Nincs kulcsod ehhez a jármûhöz!\");
        }
        else if(vehicleid == 481 || vehicleid == 509 || vehicleid == 510) return 1;
        return 1;
}
[/pawn]

[pawn]
public OnPlayerEnterVehicle(playerid, vehicleid, ispassenger)
{
        if(kulcsok[playerid] == 0)
        {
        new Float:x,Float:y,Float:z;
        GetPlayerPos(playerid,x,y,z);
        SetPlayerPos(playerid,x,y,z+3);
                SendClientMessage(playerid,0xFFFFFFAA,\"Nincs kulcsod ehhez a jármûhöz!\");
               
        }
 if(vehicleid == 481 || vehicleid == 509 || vehicleid == 510) return 0;
        return 1;
}
[/pawn]
Ha így sem jó akkor:
[pawn]
public OnPlayerEnterVehicle(playerid, vehicleid, ispassenger)
{
        if(kulcsok[playerid] == 0)
        {
        new Float:x,Float:y,Float:z;
        GetPlayerPos(playerid,x,y,z);
        SetPlayerPos(playerid,x,y,z+3);
                SendClientMessage(playerid,0xFFFFFFAA,\"Nincs kulcsod ehhez a jármûhöz!\");
               
        }
 if(vehicleid == 481 || vehicleid == 509 || vehicleid == 510) return 1;
        return 0;
}
[/pawn]
Több ötletem nincs.

[pawn]
new kulcsok[MAX_PLAYERS];
public OnPlayerStateChange(playerid, newstate, oldstate)
{
new vehicleid;
    vehicleid = GetPlayerVehicleID(playerid);
if(IsPlayerInAnyVehicle(playerid))
{
new Float:x,Float:y,Float:z;
if(kulcsok[playerid] == 0)
{
GetPlayerPos(playerid,x,y,z);
SetPlayerPos(playerid,x,y,z+3);
SendClientMessage(playerid,0xFFFFFFAA,\"Nincs kulcsod ehhez a jármûhöz!\");
}
    if(vehicleid == 481 || vehicleid == 509 || vehicleid == 510)
{
return 1;
}
}
return 1;
}
[/pawn]
Így?