Invalid date format causes system to crash

Hello experts. I'm not sure where to even start looking to resolve this problem.

In the shopping cart if a user changes the delivery date to an incorrect format it causes the system to hang. For example if the user enters a date in the past such as 03/01/2006 the correct error msg is returned. However, if they enter an invalid format like <b>0/28/2006, 0328/2006</b> a pop-up box with the "invalid date" msg continuously appears. Even after pressing "ok" it pops up over and over again.

The only way out is to terminate the application. Any help will be appreciated. Thank you