Getting UNEXPECTED_ERROR when adding new items to a sales order, but only when inside of a for loop

@NApiVersion

I'm writing a script that takes a sales order with a kit, and adds the components of the kit to the sales order and then removes the individual kit itself. I have no problem adding an item to the sales order outside of a loop, but as soon as I put it inside of a for-loop I get UNEXPECTED_ERROR.

   /**   * @NApiVersion 2.x   * @NScriptType UserEventScript   * @NModuleScope SameAccount   */  define(['N/record', 'N/search', 'N/email'], function(record, search, email) {      function afterSubmit(scriptContext) {  //        var salesOrderId = scriptContext.newRecord.id;          var salesOrderId = 536658;  //        Used to store kit components item IDs          var componentsOfKit = [];  //        Use to store quantity of each component          var componentsQTY = [];            var componentsPrices = [];            //Loads Sales Order          salesOrder = record.load({              type: record.Type.SALES_ORDER,              id: salesOrderId,              isDynamic: true          });            itemsInSalesOrder = [];          itemsCount = salesOrder.getLineCount({              sublistId: 'item'          });            //Creates array of items in sales order to be passed as parameter into searchForKit function          for(var i=0; i<itemsCount; i++){              itemsInSalesOrder.push(salesOrder.getSublistValue({                  sublistId: 'item',                  fieldId: 'item',                  line: i              }));          };