This simply means someone (you? your web developer) created a robots.txt file instructing visitors from archive.org not to create a "snapshot" of your site. Various web servers will send out automated web agents to spider through your site and either index the content (for search), archive the content. or even scrape the content for their own use. You can request these agents not to do this through the robots.txt file.
Unfortunately, bad agents will visit your site and ignore the robots.txt file. If your hosting company charges you for bandwidth, they are essentially stealing from you. Sadly, at this time it is not illegal to ignore robots.txt. So what it means is that although archive.org doesn't have a snapshot of your site, if you got a letter then you adversary likely does.
Unfortunately, bad agents will visit your site and ignore the robots.txt file. If your hosting company charges you for bandwidth, they are essentially stealing from you. Sadly, at this time it is not illegal to ignore robots.txt. So what it means is that although archive.org doesn't have a snapshot of your site, if you got a letter then you adversary likely does.