"Since about October 15, from time to time trades are rejected by Oanda due to a too high precision of the stop loss (fixed in V 1.51.9).
Setting a new stop loss of an open trade with exitLong/exitShort required that the trade already had a stop loss; it did not work for trades with no stop (fixed in V1.52.4). Workaround: enter the trade with a distant stop when you want to modify the stop loss afterwards with exitLong/exitShort."

http://zorro-trader.com/manual/en/new.htm