When I added SSL for higher security on the Wall Worm store, it broke the downloads in non-SSL pages (like when not logged in as a customer). http://wallworm.com/store/index.php?route=product/product&path=59&product_id=55
Hopefully the error will be fixed soon.
I had to remove the enforcement of SSL on the site as it was causing too many errors. For now the old non-SSL link is again the link to use. I've edited the link above.