MISSING_REQD_FLD error when SS 2.0 script triggers SS 1.0 user event script that creates child custo

Here's my scenario:

I have a custom record type that's a child of transaction records, meaning I have a List/Record field that references a transaction and I checked RECORD IS PARENT. I also made this field mandatory. Let's say the field ID of this field is custrecord_transaction. Let's also say we have a free-form text field with the ID custrecord_text. On the transaction type, I enabled child record editing.

I have a SS 1.0 user event script that creates a child record before submit. The script looks like this:

function beforeSubmit()  {      var salesorder = nlapiGetNewRecord();      salesorder.selectNewLineItem('recmachcustrecord_transaction');      salesorder.setCurrentLineItemValue('recmachcustrecord_transaction', 'custrecord_text', '1');      salesorder.commitLineItem('recmachcustrecord_transaction');  }