主题：我根据帮助中的“自定义用户与权限管理”这一章节，做一个自定义用户界面，结果，出现以下这样的错误提示？

没看出有问题，蒙一下：

Dim cmd As New SQLCommand
Dim dt As DataTable
Dim cmb As WinForm.ComboBox = e.Form.Controls("UserName")
cmd.C
cmd.CommandText = "SELECT DISTINCT Name From {用户管理}"
dt = cmd.ExecuteReader()

if dt isnot nothing then

    For Each dr As DataRow In dt.Datarows
       cmb.Items.Add(dr("Name"))
    Next
    cmb.SelectedIndex = 0

end if