product download error

WordPress version: 3.8.1
WP e-Commerce version: 3.8.13.4
Theme: ikonik lite

when i click on a product download link as a customer (eg. from post-purchase email) or as the shop owner (eg. on a prodct page) i get the following message:

“Sorry something has gone wrong with your download!”

the shop previously worked perfectly, then this problem started along with being unable to properly upload new products. i made no changes to any of the software or to the webspace prior to the error starting to happen.

any ideas appreciated.

https://www.ads-software.com/plugins/wp-e-commerce/