It sounds like you are trying to enter another opening position with a "plus" order. That's a buy plus a stop. Since you are already in a position you just need to enter a stop order only. You can do that by right clicking the button below "type" which is for order types. You will see a drop down menu and you can select either "stop limit" or "stop market". If you have any troubles entering this whatsoever please contact customer support at fxsupport@mbtrading.com or 866-558-3342.