Searching for sales orders pending fulfillment

@operator

I'm trying to get all the sales orders that are pending fulfillment and getting this error:
No Enumerated Value _pendingFulfillment for Enumerated Type TransactionStatus

Here is the C# code:

 public void GetFulfillableSalesOrders()  {      if(IsLoggedIn() == false)      {          Login();      }        TransactionSearchBasic tsb = new TransactionSearchBasic();        // Filter to only include ItemFulfillments      SearchEnumMultiSelectField tranType = new SearchEnumMultiSelectField();      tranType.@operator         = SearchEnumMultiSelectFieldOperator.anyOf;      tranType.operatorSpecified = true;      tranType.searchValue       = new string[]{ RecordType.salesOrder.ToString() };            //  Filter to only Sales Orders with a status of 'Pending Fulfillment'      SearchEnumMultiSelectField tranStatus = new SearchEnumMultiSelectField();      tranStatus.@operator         = SearchEnumMultiSelectFieldOperator.anyOf;      tranStatus.operatorSpecified = true;      tranStatus.searchValue       = new string[]{ SalesOrderOrderStatus._pendingFulfillment.ToString() };            tsb.type   = tranType;      tsb.status = tranStatus;      SearchResult results = _service.search(tsb);  }