While click add to cart button, it goes to blank screen page

While click add to cart button, it goes to blank screen page in zencart v1.5.0

URL - https://www.parkguesttickets.com/tours-excursions-c-6/ultimate-airboat-ride-at-wild-florida-adult-ages-12-p-230.html

How can we solve this?

Check in your store's /cache folder, looking for a myDebug*.log file; the most recent of those will have information that identifies the source of the error.

I have checked the cache folder. It was not showing anything. Here last updated date is "8-27-2013". I am getting confusion..

Also while click the "Add to Cart" button, it is showing this blank screen..

I am able to add to cart without a problem ...

However, you have two Add to Cart on each page ... you will notice if you try to Add 2 to the cart using the top add to cart, only one is added ... you have conflicting submits for the Top and Bottom Add to Cart so you cannot add properly with both buttons on the same page ...