Error trying to list Prestashop store products with Webservice

I am having problems trying to list the products of a prestashop store with Webservice. When I try to list all the products I get this error:

Fatal error:

  

Uncaught exception 'PrestaShopWebserviceException' with message 'This   call to PrestaShop Web Services failed and returned an HTTP status of   404. That means: Not Found. ' in C: \ xampp \ htdocs \ AppClient \ PSWebServiceLibrary.php: 85 Stack trace: # 0   C: \ xampp \ htdocs \ AppClient \ PSWebServiceLibrary.php (269):   PrestaShopWebservice- > checkStatusCode (404) # 1   C: \ xampp \ htdocs \ AppClient \ R-Products.php (215):   PrestaShopWebservice-> get (Array) # 2 {main} thrown in   C: \ xampp \ htdocs \ AppClient \ PSWebServiceLibrary.php on line 85

Any idea what the problem might be?

Thank you very much !!