I have found that when I use fixed money management for an EA I have no problems backtesting in MT4, however, if I use % of balance for money management then no trades are produced in MT4 backtesting and I get the 131 error for OrderSendError invalid lot size. When I get the error I change the money management from % to fixed lot and there are no more problems in backtesting. Can this issue be fixed so that any % lot size in a trade is adjusted to fit the broker accepted lot size?
Please check your log what is the computed size. Two most probable reasons: