Error: literal does not match format string

I have a textbox that takes a date (sStartDate) and I am trying to pass that date to my Oracle procedure but getting the following error:
ORA-01861: literal does not match format string
How do I fix it?              
C# code:
sStartDate = txtStartDate.text; DateTime date = DateTime.Parse(sStartDate); objCmd.Parameters.Add("start_date", OracleType.DateTime).Value = date.ToString("dd-MMM-yy");