Having the same problem:
>> list_orders USD BTSX
TYPE QUANTITY PRICE BALANCE COST COLLATERAL ID
================================================================================================================================
ask_order X,XXX.XXXXX BTSX 0.XXXXXXXXXXXXXXXXXXX USD / BTSXX,XXX.XXXXX BTSX XXX.XXXXX USD N/A BTSX9cEV********************
>> cancel_order BTSX9cEV*************** (hidden for privacy)
37002 unknown_market_order: unknown market order
...
bytemaster, sent you detailed exception call stack in pm, in case you need to analyze.