The virtual product plugin has a defect in it. When in the admin back office, the admin cannot modify any changes to a listing without having to upload another copy of the virtual product. It requires another upload to save the changes. The code requires the admin to re-post the zip file. This will be impossible since the user has the upload content (the admin does not have access to someone else's content on their drive to upload). 

Most probably this is required when file is required