CLR Console Application

Hello:

I have created a CLR console application in visual Studio 2005. I am trying
invoke an ASP file and save it locally. Please find code.

CString csFileName;
CLSIDFromProgID (OLESTR("InternetExplorer.Application"), &clsid);
    CoCreateInstance (clsid, NULL, CLSCTX_SERVER, IID_IUnknown, (LPVOID *)
&punk);
    punk->QueryInterface (IID_IWebBrowser2, (LPVOID *) &pWB);
    punk->Release();
    CString csFile;
    CString InvId = _T("343");
    csFile.Format(_T("http://Localhost/IMyfile/IMyfile.asp?InvId=%s"),InvId);
    bstrVal = csFile.AllocSysString();
    var.vt = VT_I4;
    var.lVal = 0;
    pWB->Navigate (bstrVal, &var, &var, &var, &var);
    SysFreeString (bstrVal);
    LPDISPATCH lpDispatch = NULL;
    hr = pWB->get_Document(&lpDispatch);
    if (SUCCEEDED(hr))
    {

    hr = lpDispatch->QueryInterface(IID_IPersistFile, (void **)&pFile);
    if SUCCEEDED(hr)
        {
          if (pFile->Save(csFileName,0)==E_FAIL)
                 Console::WriteLine(L"Unable to SaveComplete File");
            else
                hr = pFile->SaveCompleted(csFileName);
        }
        else
        {
             Console::WriteLine(L"Error in creating the Query Interface");
        }

    }
    Console::WriteLine(L"able to SaveComplete File");
    pFile->Release();
    lpDispatch->Release();
                pWB->Quit();

I have inlcuded required header files(#include <exdisp.h>,#include <mshtml.h>,
#include <atlstr.h> and #include <atltime.h>) This code works fine if debug
it step by step but If I run it whether exe in debug mode or release mode, it
throws an error that System.NullReferenceException was unhandled. It points
to code pFile->Release();
    lpDispatch->Release();

Please let me know what i am doing wrong.

Thanks in advance