[Haydz]

You've got a capital letter at the start of 'stock'

pawn Код:

Stock StartWorking(playerid) //change the uppercase S to a lowercase.
{
    if (Working[playerid] == 1) return SendClientMessage(playerid, 0xFF0000AA, "Your already on a route, so we cannot give you a new one!");
    new ID = random(sizeof(MissionData));
    new VehModel = GetVehicleModel(GetPlayerVehicleID(playerid));
    if(VehModel == 403 || VehModel == 514 || VehModel == 515)
    {
        if(MissionData[ID][Type] != 1) return StartWorking(playerid);
    }
    Working[playerid] = 1;
    PlayerMissionData[playerid][Pay] = MissionData[ID][Pay];
    return 1;
}

Yes, I tried placing an uppercase letter at the start of Stock in my script and it also crashed me. So it should solve your problem (hopefully).