WebApi保存销售订单，提示销售订单汇率为必录项!

{"Result":{"ResponseStatus":{"ErrorCode":500,"IsSuccess":false,"Errors":[{"FieldName":"","Message":"销售订单汇率为必录项!"},{"FieldName":"AbstractInteractionResult","Message":"AbstractInteractionResult.InteractionContext is null"}]},"Id":""}}

调用保存接口保存销售订单提示如上，
json如下:
[
"SAL_SaleOrder",
{"Creator":"Administrator",
"NeedUpDateFields":[],
"Model":
{"FID":0,
"FDate":"2016-03-04 16:00:29",
"FBillTypeID":{"FNUMBER":"XSDD01_SYS"},
"FReceiveAddress":"string",
"FCustId":{"FNUMBER":"CUST0001"},
"FSaleOrgId":{"FNumber":"100"},
"FSalerId":{"FNumber":"21221"},
"SAL_SaleOrder__FSaleOrderFinance":
{"FExchangeRate":1,
"FExchangeTypeId":
{"FNUMBER":"HLTX01_SYS","FNAME":"固定汇率"},
"FSettleCurrId":{"FNUMBER":"PRE001"},
"FBilltaxAmount":10000},
"SAL_SaleOrder__FSaleOrderEntry":
[
{"FMaterialId":{"FNumber":"100"},
"FDeliveryDate":"2016-03-04 16:00:31",
"FStockOrgId":{"FNumber":"100"},
"FEntryTaxRate":17,
"FStockUnitId":{"FNumber":"Pcs"},
"FUnitId":{"FNumber":"Pcs"},
"FQty":"100","FPrice":100,
"FTaxPrice":10000}
]
}
}
]

请问是什么原因啊，返回Json又没提示哪个字段