为什么 我写了rs=nothing 报错：“对象变量未设置”

        set rs=server.CreateObject("ADODB.recordset")
            sql="select * from login where user='"&user&"' and pwd='"&pwd&"'"
            rs.open sql,conn,1,1
    if not rs.eof then
               rs.close
               response.Write(index_loginmsgd)
               response.End()
        else
               rs.close
               rs.open "select * from login",conn,1,3
               rs.addnew
               rs("user")=user
               rs("pwd")=pwd
               rs("username")=username
               rs("tel")=tel
               rs.update
               rs.close
               rs=nothing
               rs=nothing
               response.Write(index_loginmsge)
    end if