Hello friend,
I believe that you cannot include .php files in a smarty include statement. You will have to get around that it by requiring the file in product.php using
Code:
require "./workshops.php"
NOTE: only if your workshops.php is saved under /yourxcart/customer/
Alter your if/else statement to fit .php style, or private message me with your if else statement and what you would like to do with it if you would like. (gramma alert! T_T)