Adding Bookmark in MS Word OLE

I'm trying to add a bookmark into an open MS Word file in code. I'm using C++ Builder 5 (I also have C++ Builder 2009). This should work via the Word.Documents.Document.BookMarks.Add( Name , Range) function but I'm having problems. Wondering if anyone can point me in the direction where I'm going wrong. Here's my code:

// ========================================================================
Variant vWordApplication;

  try
  {
    vWordApplication = Variant::GetActiveObject("word.application");
  }
  catch(...)
  {
    try
    {
      vWordApplication = Variant::CreateObject("word.application");
    }
    catch(...)
    {
      // if we got here, we were unable to create new Word object
      return;
    }
  }

 // get the documents collection
Variant vDocuments = vWordApplication.OlePropertyGet("Documents");

 // open the document in question
 Variant vDocument = vDocuments.OleFunction("Open", FileNameString);

 // make Word visible to the user
 vWordApplication.OlePropertySet("Visible", (Variant)True);

 // get a Range object of characters 1 through 10
 Variant vTenCharRange = vDocument.OleFunction("Range", (Variant)1, (Variant)10);

 // get the Document.BookMarks property collection
 Variant vBookMarks = vDocument.OlePropertyGet("BookMarks");

 // now - add a new bookmark in! Nothing seems to work.

 // NOT WORKING
vBookMarks.OleFunction("Add", (Variant)"TestName");

// ALSO NOT WORKING
vBookMarks.OleFunction("Add", (Variant)"TestName", vTenCharRange);

// ======================================================================