某行代码换个位置，原因自己琢磨一下：

Dim tr As WinForm.TreeView = e.Form.Controls("TreeView1")
Dim Cmb1 As String = e.Form.Controls("ComboBox1").Value
Dim dt As DataTable = DataTables("MPS_计划明细")
\'生成目录树
Select Case Cmb1
    Case "订单编号"
        tr.Nodes.Clear \'清空当前目录树
        tr.buildtree("MPS_计划明细","订单编号|顶层编码")
        tr.Nodes.Insert("显示所有",0) \'最顶端显示
        tr.StopRedraw()
        For Each nd As WinForm.treeNode In tr.AllNodes
            If nd.Level = 1 Then
                nd.text = nd.text & "|" & nd.DataRow("品名")
                Functions.Execute("AddChildren_MPS",nd,dt)
            End If
        Next
        tr.ResumeRedraw()
    Case "客户"
        tr.Nodes.Clear \'清空当前目录树
        tr.buildtree("MPS_计划明细","客户|订单编号|顶层编码")
        tr.Nodes.Insert("显示所有",0) \'最顶端显示
        tr.StopRedraw()
        For Each nd As WinForm.treeNode In tr.AllNodes
            If nd.Level = 2 Then
                nd.text = nd.text & "|" & nd.DataRow("品名")
                Functions.Execute("AddChildren_MPS",nd,dt)
            End If
        Next
        tr.ResumeRedraw()
    Case "产品编码"
        tr.Nodes.Clear \'清空当前目录树
        tr.buildtree("MPS_计划明细","顶层编码")
        tr.StopRedraw()
        For Each nd As WinForm.treeNode In tr.AllNodes
            If nd.Level = 0 Then
                nd.text = nd.text & "|" & nd.DataRow("品名")
                Functions.Execute("AddChildren_MPS",nd,dt)
            End If
        Next
        tr.Nodes.Insert("显示所有",0) \'最顶端显示
        tr.ResumeRedraw()
End Select