Does anyone know what this means?

I have just installed paypal and was in the shipping section to make sure i had all set ok and it give me the following

Fatal error: Cannot redeclare class ot_coupon in /home/vixenza/public_html/shop/includes/modules/order_total/ot_coupon.php on line 10


line 10 as you may see on yours is

class ot_coupon {

Any ideas guys?

Cheers

Rob