setting custom price level on line items

I am having trouble specifying a custom price level on line items when adding a sales order via SuiteTalk.

I have the following code:

                   so.itemList.item[0].price = new RecordRef();
                   so.itemList.item[0].price.type = RecordType.priceLevel;
                   so.itemList.item[0].price.typeSpecified = true;
                   so.itemList.item[0].price.internalId = "-1";

based upon a results.xml snippit of:

<tranSales: price internalId="-1" xmlns: platformCore="urn:core_2011_2.platform.webservices.netsuite.com">
  <platformCore:name> </platformCore:name>
</tranSales: price>


With this code I get the following User Error:

<platformCore:code>USER_ERROR</platformCore:code>