There was an error subscribing to the calendar.

I'm trying to add a new Calendar Subscription on my Late 2012 Mac Mini (Core i7, 16GB RAM, 320 GB free HD space) with El Capitan (version 10.11.3) , but after pasting the Calendar URL in the prompt, and clicking the Subscribe button I get the error...

There was an error subscribing to the calendar.

There was an unexpected error with the request on subscribed calendars (error -1).

Without a more descriptive error I'm not even sure where to begin. I've googled many variants of the error message along with various keywords, but have come up dry. For what it's worth, here is the URL (scrambled of course) http://www.homeaway.com/icalendar/0d5e67e37e6c4c8487a2462674ba1137.ics . I just subscribed to another calendar not 5 minutes earlier without issue.

Any ideas on what's going on or where to begin? Thanks.