I'm looking at the page of error codes: http://institutions.interactivebrok...interoperability/socket_client_c++/errors.htm There are two error codes which I use to identify un-succesful cancelation: 161 and 136. 136 = This order cannot be cancelled. 161 = Cancel attempted when order is not in a cancellable state. Order permId... there is also a generic one 135 = Can't find order with ID The purpose of this is to roll back unwanted trade. For example.... if I wanted to cancel order... but in the meantime it was filled, I want to place opposite trade... how do you guys do this?