How to modify the Stop Loss Order in a bracket Order

OrderID = ibc.ModifyOrder (OldID, Name(), "Sell", 20000, "STP", 0, "Mkt", "GTC", True);


I have placed a bracket order with only a stoploss child order. The Master order was executed and I am trying to modify the child stoploss order. This is this error message: Error 19 .COM method/function 'ModifyOrder' call failed. COM error: Type mismatch on one or more argument(s).

The error for the Modify order is listed as above, please help.