repeating auto incrementing number

I have an Access database that contains a field that stores an order id number when an order is placed. The field is auto incrementing. However, on more than one occasion I have seen two different tickets with the same number. How can this be and how can I avoid this ever happening again?
thanks alot,
ted

I don't know why that may be happening. I was wondering though if in your table that the orderID field is Indexed and and is set to {Yes (No Duplicates)} It may be something else but hope this may help.

Eric