The conversion of a varchar data type to a datetime data type resulted in an out-of-range value

<div class="col-lg-3 col-md-3" style="float: left">
               <asp:DataList runat="server" ID="dataimg" RepeatColumns="4" RepeatDirection="Horizontal" ItemStyle-CssClass="panel panel-default">
                   <ItemTemplate>
                       <li class="list-group-item list-group" style="width: 200px">
                           <asp:HyperLink ID="HyperLink1" NavigateUrl='<%# String.Concat("Img/",Eval("image")) %>'
                               Target="_blank" runat="server">
                               <img src='Img/<%#Eval("image") %>' alt="15aug" width="160px" height="160px" />
                           </asp:HyperLink>
                           <asp:Label ID="Label1" runat="server" CssClass="text text-default" Font-Size="12px" Text='<%#Eval("detail") %>'></asp:Label>
                           <%--<label id="label">
                               <a href="<%#"design.aspx?pid="+Eval("ID") %>">View Details</a></label>--%>
                       </li>
                   </ItemTemplate>
               </asp:DataList>
           </div>

protected void Unnamed1_Click(object sender, EventArgs e)
   {
       // NB: The "as" operator can return null:
       LinkButton lnk = sender as LinkButton;
       if (lnk == null)
       {
           throw new InvalidOperationException("sender is not a LinkButton!");
       }

       DateTime theDate;
       // NB: If your date is in a specific format, use TryParseExact instead.
       string format = "dd-MM-yyyy";
       if (!DateTime.TryParseExact(lnk.Text, format, null, DateTimeStyles.None, out theDate))
       {
           // The text is not a valid date:
           throw new FormatException(string.Format("The value '{0}' is not a valid date.", lnk.Text));
       }

       TextBox1.Text = lnk.Text;

       using (SqlConnection con1 = new SqlConnection(ConfigurationManager.AppSettings["str"]))
       using (SqlCommand cmd = new SqlCommand("SELECT * FROM date1 WHERE ddate = @ddate", con1))
       {
           cmd.Parameters.AddWithValue("@ddate", theDate.Date);

           DataSet ds1 = new DataSet();
           SqlDataAdapter da1 = new SqlDataAdapter(cmd);
           da1.Fill(ds1);

           dataimg.Visible = true;
           dataimg.DataSource = ds1;
           dataimg.DataBind();
       }
   }