During the import of an XML file, CSVI VirtueMart can show a notice saying:
Warning: XMLReader::readInnerXml() [xmlreader.readinnerxml]: file:///myxml.xml:22: parser error : Extra content at the end of the document in \administrator\components\com_csvivirtuemart\helpers\file\import\xml.php on line 356
When this happens, it means that your XML file is not valid. Make sure that all opened tags have a closing tag.