Date Issue in IIS7

Question

I'm using date format in dd/MM/yyyy format
When selecting from calendar i'm converting to dd/MM/yyyy format as shown below

DateTime dt = new DateTime();
dt = Convert.ToDateTime(Calendar2.SelectedDate.ToString());
string sDate = dt.ToString("dd/MM/yyyy");
txtHearingDate.Text = sDate;

I'm using IIS6 and its working fine

Now i build the website of that application and created a virtual directory in another machine having IIS7. when i run in that system, i.e, when i select
a date in that system from calendar its selecting date as dd-mm-yyyy format.
Its not converting to dd/MM/yyyy format even though i have written the code.
I have changed my system computer date format to dd/MM/yyyy format,but
still its not working