主题：TreeView累计子节点数据

 目的：通过递归算法实现子节点对应表中行的数值列的累计计算，但出现了系统错误，说明如下：

1. 数据源

2. 命令窗口的程序代码

Forms("Win1").open()
Dim tr As WinForm.TreeView = Forms("Win1").Controls("TreeView1")
Dim tb As Table = Tables("TbTree")
tr.GenerateTree(DataTables("TbTree"),"Cod","ValueA",".")  '显示ValueA，用与于程序结果核对
Forms("Win1").show()

For Each nd As WinForm.TreeNode In tr.nodes
    If nd.nodes.Count = 0 Then
        nd.ParentNode.DataRow("ValueA")+=nd.DataRow("ValueA")
        nd.ParentNode.DataRow("ValueB")+=nd.DataRow("ValueB")
    Else
        Functions.Execute("CalChild",tb,tr,nd)
        nd.ParentNode.DataRow("ValueA")+=nd.DataRow("ValueA")
        nd.ParentNode.DataRow("ValueB")+=nd.DataRow("ValueB")
    End If
Next

3. 内部函数代码

Dim tb As Table = args(0)
Dim tr As WinForm.TreeView = args(1)
Dim nd As WinForm.TreeNode = args(2)

For Each ndcd As WinForm.TreeNode In nd.nodes
    If ndcd.nodes.count=0 Then
        ndcd.ParentNode.DataRow("ValueA")+=ndcd.DataRow("ValueA")
        ndcd.ParentNode.DataRow("ValueB")+=ndcd.DataRow("ValueB")
    Else
        Functions.Execute("CalChild",tb,tr,ndcd)
        ndcd.ParentNode.DataRow("ValueA")+=ndcd.DataRow("ValueA")
        ndcd.ParentNode.DataRow("ValueB")+=ndcd.DataRow("ValueB")
    End If
Next

4. 显示结果及未知的系统错误

系统错误

但仍然能显示结果：

？？请大师指点，改正错误？？