C# Error: Arithmetic overflow error converting expression to data type datetime

You are getting this error

Arithmetic overflow error converting expression to data type datetime

becouse your date is not in a correct format.

You are are having 10.00 in time. you need to convert the . to :.

HTML

<div>
    <asp:DropDownList ID="ddlDurations" runat="server">
        <asp:ListItem Text="10.00 - 11.00" Value="10.00 - 11.00" />
        <asp:ListItem Text="11.00 - 12.00" Value="11.00 - 12.00" />
        <asp:ListItem Text="12.00 - 13.00" Value="12.00 - 13.00" />
    </asp:DropDownList>
    <asp:Button Text="Save Date" OnClick="SaveDate" runat="server" />
    <br />
    StartDate
    <asp:Label ID="lblStartDate" runat="server" />
    &nbsp;End Date
    <asp:Label ID="lblEndDate" runat="server" />
    <br />
</div>

Namespace

using System.Data;
using System.Configuration;
using System.Data.SqlClient;
using System.Globalization;

C#

protected void SaveDate(object sender, EventArgs e)
{
    string endTime = string.Empty;
    string startTime = string.Empty;
    string dropdownvalue = this.ddlDurations.SelectedItem.Text.ToString();
    string et = dropdownvalue.Split('-')[1].ToString();
    endTime = "2014-05-15 " + et.Split(' ')[1].ToString();
    startTime = "2014-05-15 " + dropdownvalue.Split(' ')[0].ToString();
    string conString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
    string sqlStatment = "INSERT INTO tblDuration(StartTime,EndTime) VALUES(@StartTime,@EndTime)";
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlCommand cmd = new SqlCommand(sqlStatment, con))
        {
            cmd.Parameters.AddWithValue("@StartTime", Convert.ToDateTime(startTime.Replace('.', ':'), new CultureInfo("en-GB")));
            cmd.Parameters.AddWithValue("@EndTime", Convert.ToDateTime(endTime.Replace('.', ':'), new CultureInfo("en-GB")));
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
        }
    }

    GetDates();


}

private void GetDates()
{
    string conString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
    string sqlStatment = "SELECT StartTime, EndTime FROM [tblDuration] Where Id = 1 ";
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlCommand cmd = new SqlCommand(sqlStatment, con))
        {
            con.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            if (reader.HasRows)
            {
                while (reader.Read())
                {
                    //where 0 is column index
                    this.lblStartDate.Text = reader.GetDateTime(0).ToString();
                    this.lblEndDate.Text = reader.GetDateTime(1).ToString();
                }
            }
            else
            {
                Response.Write("No rows found.");
            }
            reader.Close();

        }
    }
}

SQL

CREATE TABLE [dbo].[tblDuration](
	[Id] [int] IDENTITY(1,1) NOT NULL,
	[StartTime] [datetime] NOT NULL,
	[EndTime] [datetime] NOT NULL
) ON [PRIMARY]

GO