javascript runtime error

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;
using System.Collections;
using System.Timers;
using System.Web.SessionState;
using System.IO;


namespace student_management.studpro
{
public partial class WebForm3 : System.Web.UI.Page
{
int TotQus = 0;
static int count = 0;
static int viewradio = 0;
float sepmarks = 0.0f;
static int marks = 0, correct = 0;
int totalSeconds = 0, seconds = 60, minutes = 60, selectedcount = 0, originalcount = 0, crt = 0, wr = 0;

SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["aloproConnectionString"].ConnectionString);
string selected=null,choose;
string Result = null;
static String CrtAns = null, ChoiceType = null;
//string constr = "Data Source=.\\SQLEXPRESS;AttachDbFilename=C:\\Users\\Administrator\\Documents\\alopro.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";
DataTable dt;
DataSet ds;
SqlDataAdapter ad;
static int rowindex = -1;

protected void Page_Load(object sender, EventArgs e)
{

DropDownList1.Visible = true;
string noofqns = "SELECT [Questions] FROM [testsettings]";
SqlCommand cmd = new SqlCommand(noofqns, con);
con.Open();
TotQus = Convert.ToInt16(cmd.ExecuteScalar().ToString());
ds = new DataSet();
ad = new SqlDataAdapter("SELECT * FROM addsubject", con);
ad.Fill(ds,"addsubject");
dt = ds.Tables["addsubject"];
marks = (int)correct;
if (marks >= 40 && marks<=45)
{
Result = "Good";
}
else if(marks >=45)
{
Result = "Best";
}
else if (marks >= 35)
{
Result = "Better";
}
else if (marks <= 35)
{
Result = "NotBad";
}
con.Close();
if (viewradio == 0)
{
RadioInvisible();
}
else
{
RadioVisible();
}
viewradio += 1;

CheckBoxInvisible();
}

protected void Timer1_tick(object sender, EventArgs e)
{
Session["time"] = Convert.ToInt16(Session["time"]) - 1;
if (Convert.ToInt16(Session["time"]) <= 0)
{
ImageButton2.Visible = false;

RadioInvisible();
}
else
{
totalSeconds = Convert.ToInt16(Session["time"]);
seconds = totalSeconds % 60;
minutes = totalSeconds / 60;
clock.Text = minutes + ":" + seconds;
}
}
public string SelectedAnswer()
{
if (RadioButton1.Checked==true)
{
return "A";
}
else if (RadioButton2.Checked==true)
{
return "B";
}
else if (RadioButton3.Checked==true)
{
return "C";
}
else if (RadioButton4.Checked==true)
{
return "D";
}
else
{
return "nothing";
}
}
protected string ChooseAnswer()
{
if (CheckBox1.Checked)
{
choose = "A,";
}
if (CheckBox2.Checked)
{
choose += "B,";
}
if (CheckBox3.Checked)
{
choose += "C,";
}
if (CheckBox4.Checked)
{
choose += "D,";
}
return choose;
}
protected void RadioUncheck()
{
RadioButton1.Checked = false;
RadioButton2.Checked = false;
RadioButton3.Checked = false;
RadioButton4.Checked = false;
}
protected void CheckBoxUncheck()
{
CheckBox1.Checked = false;
CheckBox2.Checked = false;
CheckBox3.Checked = false;
CheckBox4.Checked = false;
}

protected void RadioInvisible()
{
RadioButton1.Visible = false;
RadioButton2.Visible = false;
RadioButton3.Visible = false;
RadioButton4.Visible = false;

}
protected void RadioVisible()
{
RadioButton1.Visible = true;
RadioButton2.Visible = true;
RadioButton3.Visible = true;
RadioButton4.Visible = true;

}
protected void CheckBoxVisible()
{
CheckBox1.Visible = true;
CheckBox2.Visible = true;
CheckBox3.Visible = true;
CheckBox4.Visible = true;
}

protected void CheckBoxInvisible()
{
CheckBox1.Visible = false;
CheckBox2.Visible = false;
CheckBox3.Visible = false;
CheckBox4.Visible = false;

}
protected void Report()
{
try
{
//con.Open();
string InsQuery = "INSERT INTO results(Dept,Testdate,Questions,Marks,Status,Username)values('" + DropDownList1.SelectedValue + "','" + DateTime.Today + "','" + TotQus + "','" + marks + "','" + Result + "','" + txtuser.Text + "')";
SqlCommand cmd2 = new SqlCommand(InsQuery, con);
con.Open();
Convert.ToInt16(cmd2.ExecuteNonQuery().ToString());
}
catch (Exception ex)
{
Response.Write(ex);
Response.Write("Try Again");
}
finally
{
con.Close();
}
}

protected void total()
{
try
{
con.Open();
if (ChoiceType == "Single")
{
selected = SelectedAnswer();
if (CrtAns == selected)
{
correct = correct + 1;
}
else
{
correct = correct - 1 / 100;
}
}
else
{
Response.Write("");
}
}
catch (Exception)
{
correct += Convert.ToInt16(sepmarks * crt) + 1;
scorestxtbox.Text = correct.ToString();
}
finally
{
//Response.Write("Wait");
con.Close();
RadioUncheck();
CheckBoxUncheck();
}
}

protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{

}

protected void ImageButton2_Click(object sender, ImageClickEventArgs e)
{
con.Open();
count += 1;
try
{
if (rowindex < TotQus)
{
rowindex = rowindex + 1;
ChoiceType = dt.Rows[rowindex]["ChooseAnswer"].ToString();
lblnoofquestions.Text = count.ToString() + " of " + TotQus;
subname.Text = dt.Rows[rowindex]["Subjectname"].ToString();
lblQuestion.Text = dt.Rows[rowindex]["Questions"].ToString();
Option1.Text = dt.Rows[rowindex]["Answera"].ToString();
Option2.Text = dt.Rows[rowindex]["Answerb"].ToString();
Option3.Text = dt.Rows[rowindex]["Answerc"].ToString();
Option4.Text = dt.Rows[rowindex]["Answerd"].ToString();
CrtAns = dt.Rows[rowindex]["Correctans"].ToString();
total();
Report();

if (ChoiceType == "Single")
{
RadioVisible();
CheckBoxInvisible();
}
else
{
RadioInvisible();
CheckBoxVisible();
}
}
else
{
ImageButton2.Visible = false;
RadioInvisible();
CheckBoxInvisible();
}
}
catch (Exception)
{
Response.Write("");

}
finally
{
//RadioUncheck();
//CheckBoxUncheck();

con.Close();
}
}

protected void ImageButton3_Click(object sender, ImageClickEventArgs e)
{
Panel1.Visible = true;
DropDownList1.Visible = false;
Labeldept.Visible = false;
txtuser.Enabled = false;
Response.Write("");
string query = "SELECT [Time] FROM [testsettings]";
SqlCommand cmd = new SqlCommand(query, con);
con.Open();
int timeget = Convert.ToInt16(cmd.ExecuteScalar().ToString());
totalSeconds = timeget * 60;
Timer1.Enabled = true;
Session["time"] = totalSeconds;
rowindex = rowindex + 1;
count = count + 1;
try
{
if (rowindex < TotQus)
{

ChoiceType = dt.Rows[rowindex]["ChooseAnswer"].ToString();
lblnoofquestions.Text = count.ToString() + " of " + TotQus;
subname.Text = dt.Rows[rowindex]["Subjectname"].ToString();
lblQuestion.Text = dt.Rows[rowindex]["Questions"].ToString();
Option1.Text = dt.Rows[rowindex]["Answera"].ToString();
Option2.Text = dt.Rows[rowindex]["Answerb"].ToString();
Option3.Text = dt.Rows[rowindex]["Answerc"].ToString();
Option4.Text = dt.Rows[rowindex]["Answerd"].ToString();
CrtAns = dt.Rows[rowindex]["Correctans"].ToString();
}
else
{
RadioInvisible();
CheckBoxVisible();
}
}

catch (IndexOutOfRangeException)
{
Response.Write("Questions Over");
}
finally
{
ImageButton3.Visible = true;
ImageButton2.Visible = true;
con.Close();
}
}


}
}