C# と VB.NET の質問掲示板

環境は
OS:Win10(64bit)
VS:2019

SharePoint上のファイルとフォルダーを検索する為、
一時的にSharePointをネットワークドライブに設定したいですが、
VBAでは以下クラスを使って問題なくできました。

Option Explicit

Private oMappedDrive As Scripting.Drive
Private oFSO As New Scripting.FileSystemObject
Private oNetwork As New WshNetwork

Private Sub Class_Terminate()
    UnmapDrive
End Sub

Public Function MapDrive(NetworkPath As String) As Scripting.folder
    Dim DriveLetter As String, i As Integer
    
    UnmapDrive
    
    For i = Asc("Z") To Asc("A") Step -1
        DriveLetter = Chr(i)
        If Not oFSO.DriveExists(DriveLetter) Then
            oNetwork.MapNetworkDrive DriveLetter & ":", NetworkPath
            Set oMappedDrive = oFSO.GetDrive(DriveLetter)
            Set MapDrive = oMappedDrive.RootFolder
            Exit For
        End If
    Next i
End Function

Private Sub UnmapDrive()
    If Not oMappedDrive Is Nothing Then
        If oMappedDrive.IsReady Then
            oNetwork.RemoveNetworkDrive oMappedDrive.DriveLetter & ":"
        End If
        Set oMappedDrive = Nothing
    End If
End Sub

そのままVBへ転用したいので、
以下のクラスをVB上で実施した結果、
「oNetwork.MapNetworkDrive(DriveLetter & ":", NetworkPath)」のところで
「The operation being request was not performed because the user has not been authenticated. HRESULT: 0x800704DC」
のエラーが発生しました。
Excel上は問題なかったのに、なんでVBでエラーが発生するか理解不能です。
どなたか問題点を教えて頂けますか？

Public Class SharePoint

    Private oMappedDrive As Scripting.Drive
    Private oFSO As New Scripting.FileSystemObject
    Private oNetwork As New IWshRuntimeLibrary.IWshNetwork_Class

    Private Sub Class_Terminate()
        UnmapDrive()
    End Sub

    Public Function MapDrive(NetworkPath As String) As Scripting.Folder
        Dim DriveLetter As String, i As Integer

        UnmapDrive()

        For i = Asc("Z") To Asc("A") Step -1
            DriveLetter = Chr(i)
            If Not oFSO.DriveExists(DriveLetter) Then
                oNetwork.MapNetworkDrive(DriveLetter & ":", NetworkPath)
                oMappedDrive = oFSO.GetDrive(DriveLetter)
                MapDrive = oMappedDrive.RootFolder
                Exit For
            End If
        Next i
    End Function

    Private Sub UnmapDrive()
        If Not oMappedDrive Is Nothing Then
            If oMappedDrive.IsReady Then
                oNetwork.RemoveNetworkDrive(oMappedDrive.DriveLetter & ":")
            End If
            oMappedDrive = Nothing
        End If
    End Sub

End Class

因みにNetworkPathはVBAもVBも同じ以下格式を使っています。
"https://XXXX.sharepoint.com/sites/XXXX/Shared%20Documents"