crystal report exporting to pdf error

using CrystalDecisions.CrystalReports.Engine;

and Add a reference to your project for the required dll, or you can install crystal report viewer to your machine

code for exporting  PDF of crystal report

http://www.codeproject.com/Tips/716161/How-to-Export-Crystal-Report-on-Button-Click-in-to

protected void Img1_Click(object sender, ImageClickEventArgs e)
        {
            SqlCommand cmd = new SqlCommand("Usp_getPersonRecords", con);
            cmd.CommandType = CommandType.StoredProcedure;
            SqlDataAdapter da = new SqlDataAdapter();
            da.SelectCommand = cmd;
            DataTable datatable = new DataTable();
            da.Fill(datatable); // getting value according to imageID and fill dataset

            ReportDocument crystalReport = new ReportDocument(); // creating object of crystal report
            crystalReport.Load(Server.MapPath("~/CrystalPersonInfo.rpt")); // path of report
            crystalReport.SetDataSource(datatable); // binding datatable
            CrystalReportViewer1.ReportSource = crystalReport;

            crystalReport.ExportToHttpResponse
            (CrystalDecisions.Shared.ExportFormatType.PortableDocFormat, Response, true, "PersonDetails");
            //here i have use [ CrystalDecisions.Shared.ExportFormatType.PortableDocFormat ] to Export in PDF

        }