主题：请问：关于窗口的问题

我使用内部数据源设计了一个窗口，然后，以同样的代码、同样的方式在外部数据源中设计了一个同样的窗口，结果总是显示：未将对象引用设置到对象的实例。，是怎么回事呢？

Dim dtb As New DataTableBuilder("分账库存统计")
dtb.AddDef("货物大类", Gettype(String))
dtb.AddDef("客户名称", Gettype(String))
dtb.AddDef("货物种类", Gettype(String))
dtb.AddDef("日期", Gettype(Date))
dtb.AddDef("库存", Gettype(Decimal))
dtb.Build()
For Each nm() As String In DataTables("进出库信息记录").GetValues("客户名称|货物种类")
    Dim dr As DataRow = DataTables("分账库存统计").AddNew()
    dr("客户名称") = nm(0)
    dr("货物种类") = nm(1)
    Dim mr As DataRow
    mr = DataTables("进出库信息记录").find("[客户名称] = '" & nm(0) & "' And[货物种类] = '" & nm(1) & "'","[_SortKey] Desc")
    dr("日期") = mr("日期")
    dr("库存") = mr("库存")
    dr("货物大类") = mr("货物大类")
Next
MainTable= Tables("分账库存统计")
Dim Filter As String
With e.Form.Controls("ComboBox1")
    If .Value IsNot Nothing Then
        Filter = " 货物大类 = '" & .Value & "'"
    End If
End With
With e.Form.Controls("DateTimePicker1")
    If .Value IsNot Nothing Then
        If Filter >"" Then
            Filter = Filter & " And "
        End If
        Filter = Filter & "日期 >= #" & .Value & "#"
    End If
End With
With e.Form.Controls("DateTimePicker2")
    If .Value IsNot Nothing Then
        If Filter >"" Then
            Filter = Filter & " And "
        End If
        Filter = Filter & "日期 <= #" & .Value & "#"
    End If
End With
If Filter > "" Then
    Tables("分账库存统计").Filter = Filter
End If
Dim g As New Subtotalgroup
g = New Subtotalgroup
g.GroupOn = "客户名称"
g = New Subtotalgroup
g.Aggregate = AggregateEnum.Sum
g.GroupOn = "货物大类"
g.TotalOn = "库存"
g.Caption = "{0} 小计"
With Tables("分账库存统计")
    .SubtotalGroups.Add(g)
End With
g = New Subtotalgroup
g.Aggregate = AggregateEnum.Sum
g.GroupOn = "*"
g.TotalOn = "库存"
g.Caption = "总计"
With Tables("分账库存统计")
    .SubtotalGroups.Add(g)
    .Subtotal()
End With
With Tables("分账库存统计")
    .MergeMode = MergeModeEnum.free
    .MergeCols.Add("货物大类")
    .MergeCols.Add("客户名称")
    .AllowMerge = True
End With

在内部数据源的情况下，点击窗口按钮就可以，但是把这个代码换到外部数据源中就会显示：未将对象引用设置到对象的实例。请大师指点下，问题出在哪里呢？

果然是大神，问题就是出在这里。太感谢你了