主题：做“目录树形式的授权”出现 这样的错误

做“目录树形式的授权”出现 这样的错误，afterload事件代码如下：

Dim trv1 As WinForm.TreeView = e.Form.Controls("TreeView1")
Dim trv2 As WinForm.TreeView = e.Form.Controls("TreeView2")
Dim cmd As New SQLCommand
cmd.C
trv1.BuildTree("授权","分组|权限")
For Each u As UserInfo In Users
    If u.Type = UserTypeEnum.User Then
        If trv2.Nodes.Contains(u.Group) = False Then
            trv2.Nodes.Add(u.Group)
        End If
        trv2.Nodes(u.Group).Nodes.Add(u.Name)
    End If
Next
Trv1.Nodes(0).Expand()
trv2.ExpandAll()