faceing exception as .. Conversion failed when converting date and/or time from character string.

i provide u the complete code... may be then you can help..

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.Timers;
using System.Data;
using System.Text;
using System.Drawing;

public partial class COMPLIANCE_CALENDAR : System.Web.UI.Page
{
SqlConnection cn = new SqlConnection("server='fre-ggn-fstest\\sharepoint'; database = 'DMS1'; integrated security = 'true';");
SqlDataAdapter sda,sda1;
SqlCommand cmd;
DataSet ds;


string s;
int i;

protected void Page_Load(object sender, EventArgs e)
{
cn.Open();


s = Session["sessFirstName"].ToString(); // here i m getting the user id from login page

alreadyExists();
// getCompName(); // here i m calling the function that will give me the company name in the label

//LblCompName.Text = s;
}



public void alreadyExists() // function to check the existing records
{


string str = "select due_date from mConfirm where due_date BETWEEN '"+DateTime.Now+"' AND due_date";

sda1 = new SqlDataAdapter(str, cn);
ds = new DataSet();
sda1.Fill(ds);
// string d = ds.Tables[0].Rows[0].ItemArray[0].ToString();
string d = "";
if (ds != null && ds.Tables[0].Rows.Count > 0)
d = Convert.ToString(ds.Tables[0].Rows[0].ItemArray[0]);



if (( DateTime.Today - Convert.ToDateTime(d)).TotalDays <= 2)
{
LblAlreadyExists.ForeColor = System.Drawing.Color.Red;
LblAlreadyExists.Text = "Already Under Process...!!!! you can not proceed";
BtnConfirmd.Enabled = false;
CHKConfirmed.Enabled = false;
}
else
{
BtnConfirmd.Enabled = true;
CHKConfirmed.Enabled = true;
LblAlreadyExists.ForeColor = System.Drawing.Color.Green;
LblAlreadyExists.Text = "You can proceed with the process";
LblDateto.Text = DateTime.Now.ToString(); // showing the time on the page
LblDatetill.Text = DateTime.Now.AddDays(2).ToString();
LblTodayDate.Text = DateTime.Now.ToString();

getCompName();
}


}




public void getCompName()
{
string str = "select comp_name from mCompnay JOIN temp ON ( mCompnay.comp_code = temp.CompCode ) WHERE emp_code='" + s + "'";

sda = new SqlDataAdapter(str, cn);
ds = new DataSet();
sda.Fill(ds);

LblCompName.Text = ds.Tables[0].Rows[0].ItemArray[0].ToString();
}

protected void BtnConfirmd_Click(object sender, EventArgs e)
{

string str = "select doc_id from tdocument td JOIN temp te ON ( td.emp_code = te.emp_code ) where te.emp_code='" + s + "'";
sda = new SqlDataAdapter(str, cn);
ds = new DataSet();
sda.Fill(ds);

string did = ds.Tables[0].Rows[0].ItemArray[0].ToString(); // storing the doc_id here in the variable


if (CHKConfirmed.Checked == true)
{

string str1 = "insert into mConfirm (doc_id,emp_id,confirm_status,assigned_date,due_date) values(@doc_id,@emp_id,@confirm_status,@assigned_date,@due_date)";

cmd = new SqlCommand(str1, cn);
cmd.Parameters.Add("@doc_id", SqlDbType.Int).Value = did;
cmd.Parameters.Add("@emp_id", SqlDbType.Int).Value = s;
cmd.Parameters.Add("@confirm_status", SqlDbType.VarChar).Value = "Confirmed";
cmd.Parameters.Add("@assigned_date", SqlDbType.Date).Value = LblTodayDate.Text;
cmd.Parameters.Add("@due_date", SqlDbType.Date).Value = LblDatetill.Text;

cmd.ExecuteNonQuery();

LBLConfirmed.ForeColor = System.Drawing.Color.Green;
BtnConfirmd.Enabled = false;
LBLConfirmed.Text = "You Have Confirmed and saved the details";