Try, Catch not Working c#

Displays error message to user from the try block.
Does not execute the catch block.


What should I change?

        try
        {
            strResearchSiteSQL = "SELECT ResearchSiteID FROM PerfCriteria WHERE UserID = '" + strUserID + "'";
            string strResearchSitePref = GetColValue(conStockSelect, strResearchSiteSQL, "ResearchSiteID");
            int intResearchSitePref = int.Parse(strResearchSitePref);  // Error here
        }

//Displays error message to user.
//Does not execute the catch block
        catch (SmtpException err)
        {
            Session["StackTrace"] = err.StackTrace;
            Session["Message"] = err.Message;
            Session["Data"] = err.Data.ToString();
            Session["Source"] = err.Source;
            Session["ErrProcName"] = "cmdSend_Click";
            Response.Redirect("~/ErrorHandling/ShowError.aspx");
        }