'String was not recognized as a valid DateTime’ error in Ajax calendar

Hi folks, I have managed to get the Ajax calendar working ok, but now I have a new problem'String was not recognized as a valid DateTime.’

If I type the date in the textbox like so 17/11/2014 it work ok, but if I select it from the Ajax calendar I receive the following error

‘String was not recognized as a valid DateTime’

The Ajax calendar does place the same date format systle in the textbox like 17/11/2014

code below

cmd.Parameters.Add("@FittingDate", SqlDbType.Date).Value = Convert.ToDateTime(txtFittingDate.Text);