主题：[求助]无法动态加载来自SQL SERVER的表

我参考"动态加载数据的例子",想动态加载来自SQL SERVER的表:tab_wjk.但是主窗口的afterload中的代码,测试时报错,请问是什么原因.请帮我检查一下错在哪里?还是外部表的代码不一样?
窗口afterload代码如下:
Dim cmd As New SQLCommand
Dim dt As DataTable
cmd.CommandText = "SELECT DISTINCT 分类号,保管期限,年度 From {tab_wjk}"
dt = cmd.ExecuteReader()
Dim trv As WinForm.TreeView = e.Form.Controls("TreeView1")
trv.BuildDataTree(dt, "","分类号", "保管期限","年度")

NodeMouseDoubleClick的代码如下:
Dim Value()As String
Dim Filter As string
Value = e.Node.FullPath.Split("\")
Select Case e.Node.Level
    Case 0
        Filter ="[分类号] = '" & Value(0) & "'"
    Case 1
        Filter ="[分类号] = '" & Value(0) & "' And [保管期限] = '" & Value(1) & "'"
    Case 2
        Filter ="[分类号] = '" & Value(0) & "' And [保管期限] = '" & Value(1) & "' And [年度] = '" & Value(2) & "'"
        End Select
DataTables("tab_wjk").LoadFilter = Filter
DataTables("tab_wjk").Load()

窗口afterload代码改成如下还是报错:

Dim cmd As New SQLCommand
Dim dt As DataTable
cmd.CommandText = "SELECT DISTINCT 分类号,保管期限,年度 From tab_wjk"
dt = cmd.ExecuteReader()
Dim trv As WinForm.TreeView = e.Form.Controls("TreeView1")
trv.BuildDataTree(dt, "","分类号", "保管期限","年度")

SELECT DISTINCT 分类号,保管期限,年度 From tab_wjk 这段代码我测试过了,是没问题的.是不是其它代码有问题?