sql="select * from [User] where UserName='"&user&"'"    
if rec.eof then

rec是啥???

没有连接数据库

<%
    if request.Form("ok")="提交" then
        if  session("username")="" or session("user_level")<>"C" then
            response.Write("<center>你无权执行该操作")
            response.Write("【<a href='vbscript:history.go(-1)'>返回</a>】</center>")
            response.End()
        end if
        level=request.Form("r1")
        user=trim(request.Form("txtname")
        sql="select * from [User] where UserName='"&user&"'"    
        set rec=Server.CreateObject("ADODB.Recordset")
        rec.Open sql,数据源,1,3
        if rec.eof then
            response.Write("<center>此用户不存在"）
            response.Write("【<a href='vbscript:history.go(-1)'>返回</a>】</center>")
            response.End()
        end if
    end if 
%>