VBS Error when saving a Word file

VBS script. I'm trying to save a Word file from doc format to docx format. If I do not specify the extension of the saved file, WSH returns the error "Invalid file name" 800A1420. If you specify the docx extension, then "The file type and extension are not compatible" 800A18696. I set the second parameter: file type, tried SaveAs2. The situation has not changed. I understand that I am doing something wrong, but what is not clear.

Option Explicit
Const msoFileDialogOpen  = 1
Const wdDoNotSaveChanges = 0
Dim strText
Dim strPath
Dim strFileName
Dim strFileNameMask
strPath     = "C:\Documents and Settings\User\Мои документы\"
strFileNameMask = "*.doc"
strFileName = "A1.docx"
With WScript.CreateObject("Word.Application")
    .Visible = True
    With .FileDialog(msoFileDialogOpen)
        .AllowMultiSelect = False
        .InitialFileName  = strPath & strFileNameMask
        If .Show() = -1 Then
            With .Application.Documents.Open(.SelectedItems.Item(1))
                strText = .Range.Text
                    .SaveAs strPath & strFileName
            End With
        End If
    End With
    .Quit wdDoNotSaveChanges
End With
WScript.Quit