[Konstantinos]

I guess it's because of this:

pawn Код:

profit = (percent * BoxerBid[pBoxer[playerid]]) / 10000;

If pBoxer[playerid] is -1, it will cause the run time error. However, without the debug info - it's not 100%.
Check if pBoxer[playerid] is not -1 and then use it inside BoxerBid array.