[Konstantinos]

OnPlayerEnterVehicle is called when a player starts to enter a vehicle. In that time (the player is not in the vehicle yet), you call CarLevel that it tries to get the player's vehicleid however it returns -1 because they are not in vehicle yet.

pawn Код:

public OnPlayerStateChange( playerid, newstate, oldstate )
{
    if( newstate == PLAYER_STATE_DRIVER && oldstate == PLAYER_STATE_ONFOOT )
    {
        TextDrawShowForPlayer(playerid, carname);
        new string[64];
        format(string, sizeof(string), "Car Name:%s~n~Max Speed:240~n~Level:%d", VehicleName[GetVehicleModel(vehicleid) - 400],CarLevel(playerid));
        TextDrawSetString(carname,string);
    }
    return 1;
}

stock CarLevel(playerid)
{
    new vehicleid = GetPlayerVehicleID(playerid);
    if(GetVehicleModel(vehicleid) == 411) return 10;
    else if(GetVehicleModel(vehicleid) == 451) return 2;
    return 0;
}