[Neil.]

pawn Код:

public OnPlayerEnterVehicle(playerid, vehicleid, ispassenger)
{
    new ownername[50];
    new player1;
      new owner;
    owner = AVehicleData[vehicleid][Owner];// symbol is assigned a value that is never used: owner
    GetPlayerName(player1, ownername, sizeof(ownername));
    if(!strcmp(owner,ownername , false))//argument type mismatch(argument 1)
    {
        new string[128];
        format(string,sizeof(string), "You are not the owner of this vehicle");
        SendClientMessage(playerid, 0x0FF0000AA, string);
    }
return 1;
}

See errors above