getLineItemCount for custom records

Hello,

I created a custom record which has ID customrecord_new, and add a field of type list and link it with the customer list and check parent check box. so the records submitted by the customer appears as a sublist in customer record.

now, from client script on Page Init Function applies to customer, I want to retrieve the records number that submitted by current customer, I tried the following script

var cur_user = nlapiLoadRecord('customer', nlapiGetRecordId());
var new_count = cur_user.getLineItemCount('customrecord_new');
alert(new_count');

but it always alerts 0 even if the customer have more

Is the wrong in the script?