Hi Mukesh,
Your first parameter is causing an overflow exception. The value after the first colon of "001:33:56:00" is an hour value and it must be less than 24 (yours is 33). Please correct it and trap it using Try-Catch:
try
{
olst.TotleQcDuration = olst.Reports.Aggregate(TimeSpan.Zero, (subtotal, t) => subtotal.Add(TimeSpan.Parse(t.Duration))).ToString();
}
catch (OverflowException)
{
MessageBox.Show("A value in the string exceeds a legitimate value.");
}