ASP.Net Convert ToDateTime Error: There is an unknown word starting at index 0

The string was not recognized as a valid DateTime. There is an unknown word starting at index 0.

Getting error below line.

cmd.Parameters.AddWithValue("@D_Date", Convert.ToDateTime(date));

private void Insert(DateTime inttime,DateTime outtime,string  date)
{
    using (SqlCommand cmd = new SqlCommand("Sp_Get_Absent", con))
    {
        cmd.Parameters.AddWithValue("@Action", "Update");
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@EmpID", lbid.Text);
        cmd.Parameters.AddWithValue("@INTIMe", inttime);
        cmd.Parameters.AddWithValue("@OutTime", outtime);
        cmd.Parameters.AddWithValue("@D_Date", Convert.ToDateTime(date));
        con.Open();
        cmd.ExecuteNonQuery();
        ScriptManager.RegisterStartupScript(this, this.GetType(), "alert", " alert('Time  saved sucessfully');", true);
        con.Close();
    }
}