数据库查询错误 rs.open

<%  dim currentpage,id,page_total,i,gcpnum,rksl,cksl,j
       sql="select * from product order by id desc"
    Set rs = Server.CreateObject("ADODB.RecordSet")
    rs.open sql,conn,1,1
    if not rs.eof then
        do while not rs.eof
            gcpnum=rs("cpnum")
            
            response.write gcpnum
               sqlrk="select sl from buy where cpnum = "& gcpnum
            response.write sqlrk

            Set rs1 = Server.CreateObject("ADODB.RecordSet")
            rs1.open sqlrk,conn,1,1      
...
%>
请高手帮我看一下，调试时显示
Microsoft JET Database Engine (0x80040E10)
至少一个参数没有被指定值。
/22.asp, 第 19 行
（第19行是贴出的最后一行）