Crystal report not displaying

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CrystalReports

In my web application I have used crystal reports of Version=13.0.2000.0
I have hosted this web application on the IIS7 and we are using this application internally through the LAN network.
My application contains 10 types of reports and there are 200 simultaneous users of the application.
Initially all crystal reports works fine but after some hours (i.e. 12-15 hrs) not a single report opens up. After that I have to restart the IIS server and then after it again starts working fine. Everyday I have to go through this process. I really don't know what is happening. Because it doesn't show any types of error.

Here are the some points regarding my web application.
1) Web application is created by using Visual Studio 2010 and target framework is 4.0
2) I am using Crystal Report Version = 13.0.2000.0
3) To design the report I have created typed data set and added fields on the report.
After that while binding the report I am fetching data from the database and assigning the data source to the report.

The code I am using is as follows-

private void Show_Monthly_Report()
{
int tmp_convert_int = 0;
int EmpId = (int.TryParse(Convert.ToString(HttpContext.Current.Session["EmpId"]), out tmp_convert_int) ? tmp_convert_int : 0);
try
{

#region Monthly Log Data Table
DataTable dt = new DataTable();

dt.Columns.Add("emp_id", typeof(string));
dt.Columns.Add("emp_full_name", typeof(string));
dt.Columns.Add("checkin_datetime", typeof(string));
dt.Columns.Add("checkout_datetime", typeof(string));

bll_emp_BRB_break_log obj_bll_emp_BRB_break_log = new bll_emp_BRB_break_log();
obj_bll_emp_BRB_break_log.Get_Details_Of_Monthly_BRB_Log(EmpId, Convert.ToDateTime(txt_from_date.Text.Trim()), Convert.ToDateTime(txt_to_date.Text.Trim()));

for (int i = 0; i < obj_bll_emp_BRB_break_log.Items.Count; i++)
{
DataRow row = dt.NewRow();

row["emp_id"] = Convert.ToString(obj_bll_emp_BRB_break_log.Items[i].emp_id);
row["emp_full_name"] = Convert.ToString(obj_bll_emp_BRB_break_log.Items[i].emp_full_name);
row["checkin_datetime"] = Convert.ToString(obj_bll_emp_BRB_break_log.Items[i].checkin_datetime);
row["checkout_datetime"] = Convert.ToString(obj_bll_emp_BRB_break_log.Items[i].checkout_datetime);

dt.Rows.Add(row);
}
#endregion

ReportDocument rptDoc = new ReportDocument();

// Your .rpt file path will be below
rptDoc.Load(Server.MapPath("../Reports/rpt_Monthly_BRB.rpt"));

//set dataset to the report viewer.
rptDoc.SetDataSource(dt);

crptv_monthly_brb.ReportSource = rptDoc;

//rptDoc.Dispose();
dt.Clear();
dt.Dispose();
}
catch (Exception ex)
{

}
}