调用webapi保存报错

调用webapi保存报错
{"Result":{"ResponseStatus":{"ErrorCode":500,"IsSuccess":false,"Errors":[{"FieldName":"After parsing a value an unexpected character was encountered: \". Line 1, position 211.","Message":" 在 Newtonsoft.Json.JsonTextReader.ParsePostValue(Char currentChar)\r\n 在 Newtonsoft.Json.JsonTextReader.ReadInternal()\r\n 在 Kingdee.BOS.JSON.JSONObjectConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)\r\n 在 Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueNonProperty(JsonReader reader, Type objectType, JsonContract contract)\r\n 在 Newtonsoft.Json.JsonSerializer.Deserialize[T](JsonReader reader)\r\n 在 Kingdee.BOS.JSON.JSONObjectConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)\r\n 在 Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueNonProperty(JsonReader reader, Type objectType, JsonContract contract)\r\n 在 Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)\r\n 在 Kingdee.BOS.JSON.JSONObject.Parse(String json)\r\n 在 Kingdee.BOS.WebApi.FormService.Save.Revole()\r\n 在 Kingdee.BOS.WebApi.FormService.Save.Execute()\r\n 在 Kingdee.BOS.WebApi.FormService.BillOperationService.ExecuteOperation(FormOperation op, String data)","DIndex":0}],"SuccessEntitys":[],"SuccessMessages":[]}}}
不懂是什么原因？