Searching 2 Custom Record, as Parent & child

Dear support,

I created two custom record.
Record PromoDiscount as parents, record QuantityItem as a child.

Record PromoDiscount (Parent) [customrecord_promo_discount]
- ID PromoDiscount
- Customer    [custrecord_pd_customer]
-  DateFrom (datetime) [custrecord_pd_valid_from]
  - DateTo (datetime) [custrecord_pd_valid_to]
Record QuantityItem (Child) [customrecord_quantity_item]
- Item (list item) [custrecord_qty_item]
- Unit (list unit) [custrecord_qty_unit]
-QtyFrom (int) [custrecord_qty_from]
- QtyTo (int) [custrecord_qty_to]
- Discount (int) [custrecord_qty_discount]

When I create SearcRecord, I can't filter Promodiscount with field item and QtyFrom,  and result Error. .

 var filters = new Array();  filters[0] = new nlobjSearchFilter('custrecord_pd_customer', null, 'anyof', 21634);  filters[1] = new nlobjSearchFilter('custrecord_pd_valid_from', null, 'onorbefore','16/7/2012');  filters[2] = new nlobjSearchFilter('custrecord_pd_valid_to', null, 'onorafter', '16/7/2012');  filters[3] = new nlobjSearchFilter('custrecord_qty_item', 'recmachcustrecord_qty_promo_discount', 'anyof','2809')  filters[4] = new nlobjSearchFilter('custrecord_qty_from', null, 'greaterthanorequalto',1);  filters[5] = new nlobjSearchFilter('custrecord_qty_to', null, 'lessthanorequalto', 10);  filters[6] = new nlobjSearchFilter('isinactive', null, 'is', 'F');    var columns = new Array();  columns[0] = new nlobjSearchColumn('custrecord_pd_customer');  columns[1] = new nlobjSearchColumn('custrecord_pd_valid_from');  columns[2] = new nlobjSearchColumn('custrecord_pd_valid_to');    var results = nlapiSearchRecord('customrecord_promo_discount', null, filters, columns);