主题：百思不得其解

出错图：

此主题相关图片如下：11.jpg

代码

DataColChanged:

　Dim dr As DataRow = e.DataRow
Select Case e.DataCol.Name
    Case "市场片区_省市"
        dr("市场片区_市") = Nothing
        dr("市场片区_县市") = Nothing

　        dr("市场代码") = Nothing
    Case "市场片区_市"
        dr("市场片区_县市") = Nothing
        dr("市场代码") = Nothing
    Case "市场片区_县市"
        Dim sss As String
        Dim xss As String
        Dim qs As String
        sss = dr("市场片区_市")
        xss = dr("市场片区_县市")
        sss = sss.SubString(0,2)
        xss = xss.SubString(0,2)
        sss = getpy(sss,True)
        xss = getpy(xss,True)
        qs = sss.ToUpper() & xss.ToUpper()
        dr("市场代码") =  qs
        Dim khdm As new SQLCommand
        khdm.C
        khdm.CommandText = "select count(*) from {编号} where [前缀] =  '"& qs &"' "
        If khdm.ExecuteScalar = 0 Then
        Dim ww As String = "客户档案"
            khdm.CommandText = "insert into 编号(表名,前缀,顺序号) values('"& ww &"','"& qs &"',1)"
            khdm.ExecuteNonQuery
        End If
End Select

数据修改变动时：就出现这个错误