ICalendar and Outlook opeing as node For Add to Cal Module Even After Clearing Caches
I'm a maintainer of the Add To Cal module. It turns out that this is in fact a bug, which we're patching right now.

Until the patch is released, you can fix the issue by downloading and enabling the Entity module on your site. The patch will add this as a dependency to Add To Cal.

Here's the issue on drupal.org: https://www.drupal.org/node/1744684#comment-9056553

EDIT: The 1.x-dev version now includes this bug fix, and it will be included in the beta4 release.