MSXML插入节点，release时出错

TCHAR * szPath = new TCHAR [MAX_PATH];     //存放选择的目录路径 
CString str; ZeroMemory(szPath, sizeof(szPath));    BROWSEINFO bi;   
bi.hwndOwner = m_hWnd;   
bi.pidlRoot = NULL;   
bi.pszDisplayName = szPath;   
bi.lpszTitle = L"请选择共享的目录：";   
bi.ulFlags = 0;   
bi.lpfn = NULL;   
bi.lParam = 0;   
bi.iImage = 0;   
//show the dialog to choose the dir
LPITEMIDLIST lp = SHBrowseForFolder(&bi);    if(lp && SHGetPathFromIDList(lp, szPath))   
{
m_OwnerListBox->Add(szPath,  AfxGetApp()->LoadIcon(IDI_FLDS));
//读取XML
MSXML2::IXMLDOMDocumentPtr spXMLDoc;
spXMLDoc.CreateInstance(__uuidof(MSXML2::DOMDocument30));
spXMLDoc->load(L"config.xml");
MSXML2::IXMLDOMElementPtr spRoot = spXMLDoc->documentElement; 
MSXML2::IXMLDOMNodePtr spNewNode = spRoot->selectSingleNode(L"/Win-DMS/SharedFolders")->appendChild(
spXMLDoc->createNode(_variant_t(NODE_ELEMENT), L"Folder", L"")
); //给node2创建新子节点childnode3
spNewNode->text = szPath;
spXMLDoc->save(_variant_t(L"config.xml")); spNewNode->Release();
spRoot.Release();
spXMLDoc.Release();

}在Release()的时候出错，求大神指教