[Konstantinos]

That is wrong:

pawn Код:

Player[MAX_PLAYER_NAME]

It should be:

pawn Код:

Player[playerid]

and you don't have to use "else if":

pawn Код:

if(GetPlayerVehicleID(playerid) != Player[playerid])
{
    RemovePlayerFromVehicle(playerid);
    SendClientMessage(playerid, COLOR_RED, "To nie twуj pojazd , wysiadaj");
}
else
{
    // code.. the vehicle is for that player
}