treeview节点重命名

以下是实现的代码，我通过下拉菜单将treeview节点重命名后，再将xml文件中对应的节点名称也修改过来，可是xe.InnerText = xmlNode.InnerText老是出现错误，不知怎么回事，请教啊


Private Sub 重命名ToolStripMenuItem_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles 重命名ToolStripMenuItem.Click

TreeView1.LabelEdit = True

If Not TreeView1.SelectedNode Is Nothing Then
str = TreeView1.SelectedNode.Text
i = TreeView1.SelectedNode.Index
End If

End Sub

Private Sub TreeView1_AfterLabelEdit(ByVal sender As Object, ByVal e As System.Windows.Forms.NodeLabelEditEventArgs) Handles TreeView1.AfterLabelEdit

If Not TreeView1.SelectedNode Is Nothing Then

Dim doc As XmlDocument = New XmlDocument
Dim xmlNode As XmlNode
Dim xe As XmlElement

doc.Load("E:\文本文件\title.xml")
xmlNode = doc.SelectSingleNode(str)

xe = doc.CreateElement(TreeView1.SelectedNode.Text)
xe.InnerText = xmlNode.InnerText
xe.ParentNode.ReplaceChild(xe, xmlNode)
doc.Save("E:\文本文件\title.xml")

End If

TreeView1.LabelEdit = False

End Sub