Server Error in '/' Application.

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Line 264:            string sql = "select repeats,starttag,endtag from tags where name='" + tagename + "'";
Line 265:            OleDbDataReader dr = con.DrSelect(sql, null);
Line 266:            if (dr.Read())
Line 267:            {
Line 268:                string sql_ = "select top " + topnums + " a.title,a.titlebold,a.titlecolor,a.website,a.htmlurl,a.picSmall,a.describe,a.dates,b.infoname,a.fid,a.cid,a.id from " + param[2] + " as a,info_class as b where a.cid=b.id and a.cid=" + fid + "  and a.state>0 and a.info_state=2 order by a.state desc,a.dates desc, a.sortnum desc, a.id desc";//and a.hot>0 and a.tgstate>0 

[NullReferenceException: Object reference not set to an instance of an object.]
   jss_fc.JSSMethods.mt_friendhref_(String tagename, OperateDB con, String[] param) in d:\website\www.aitg.cn2\App_Code\jss_fc\JSSMethods.cs:266
   jss_fc.JSSMethods.TAGES_SINGLE(String tagename, OperateDB con, String[] param, String[] idsparam) in d:\website\www.aitg.cn2\App_Code\jss_fc\JSSMethods.cs:253
   news.Page_Load(Object sender, EventArgs e) in d:\website\www.aitg.cn2\news.aspx.cs:96
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +85
   System.Web.UI.Control.OnLoad(EventArgs e) +74
   System.Web.UI.Control.LoadRecursive() +120
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2847