single-row subquery returns more than one row

Hi Team,
We are doing RIB customization on version 14.0.1:
Error : ORA-01427: single-row subquery returns more than one row
We are facing issue with XMRCHHRCLS family and below is the XML file
<?xml version="1.0" encoding="utf-8"?>
<XMrchHrClsDesc>
   <class>4544</class>
   <class_name>Class V14 Testing</class_name>
   <class_vat_ind>Y</class_vat_ind>
   <dept>20</dept>
<ExtOfXMrchHrClsDesc>
  <XMrchHrClsVAT>
    <vat_region>1000</vat_region>
    <vat_code>100001</vat_code>
        <vat_type>B</vat_type>
      </XMrchHrClsVAT>
      <XMrchHrClsVAT>
    <vat_region>2000</vat_region>
    <vat_code>200001</vat_code>
        <vat_type>B</vat_type>
  </XMrchHrClsVAT>
      <XMrchHrClsVAT>
    <vat_region>3000</vat_region>
    <vat_code>300001</vat_code>
        <vat_type>B</vat_type>
  </XMrchHrClsVAT>