This is a bug fix related to download virtual products from the command history of customer accounts and email sent to the customer.
Some virtual products can be downloaded but other posters error well.
The shop contains about 150 virtual products to check and correct. The problem may be the MySQL database.
Store in Prestashop 1.5.3 on shared hosting OVH / OVH private Sql
Once this bug fixed other developments will be provided on this shop and others. Many projects.