返回声明中的vba'91'错误

Question

我写的以下功能无法正常工作。我得到臭名昭着的'91'对象变量或With块变量没有设置错误在我要返回对象的块的最后一行。我不明白为什么，因为我的输入节点确实具有所需id的子节点。 MsgBox告诉我实际找到了节点，因此设置了变量res。我仍然得到'91'错误。

    Private Function getElementById(root As MSXML2.IXMLDOMNode, id As String) As MSXML2.IXMLDOMNode

    Dim Children As MSXML2.IXMLDOMNodeList
    Dim Child As MSXML2.IXMLDOMNode
    Dim res As MSXML2.IXMLDOMNode
    Dim found As Boolean
    found = False

    If (root.HasChildNodes = True) Then

        Set Children = root.ChildNodes

        For a_counter = 0 To (Children.Length - 1)

            Set Child = Children.Item(a_counter)

            If Child.Attributes.getNamedItem("id").Text = id Then

                Set res = Child
                found = True
                MsgBox "Found"

            End If

        Next a_counter

        If found = False Then
            MsgBox "Not Found"
            res = Nothing
        End If

    Else

        Set res = Nothing
        MsgBox "No Children"

    End If

    getElementById = res

    End Function