Files uploaded to Calender validator giving ""Calendar can't read this imported calendar file" error

I had the same problem with a.ics file downloaded from a web site. It wasn't anything to do with extended attributes such as quarantine. I upload my file to the icalendar validator, which flagged several errors. Fixing the first error by adding a CR to the end of each line, and a LF at the end of the file, solved the problem. I've reported it as a bug to the web site.

[Re-Titled By Moderator]