[Vince]

It's fairly obvious that it's related to this part;

pawn Код:

if(GettingSpectated[playerid] != INVALID_PLAYER_ID) // suppose this contains 999. Obviously not equal to INVALID_PLAYER_ID so this is true
    {
        new spectator = GettingSpectated[playerid]; // spectator now contains 999
        if(!IsPlayerConnected(spectator)) // player 999 does not exist and is therefore not connected so this is also true
        {
            GettingSpectated[playerid] = 999;
            Spectate[spectator] = 999; // 'spectator' is still 999, which is an invalid array index, hence causing the OOB error
        }
        // bunch of code
    }

Why do you use INVALID_PLAYER_ID in one place and 999 in another?