I tried this as a network-wide activation on my site(s).
Then put an event post on the blog of my root, which worked (apart from the date always showing up as "Day 00 Month Year" - no matter what date I picked! (ie the day always shows up as "00").
Then I noticed it was interfering with one of my blogs on a subdirectory of the main domain - it showed no posts or content, just my blog header and "Events Calendar".
Deactivated as network plugin, and reactivated just on the root. Now the blog on my subdirectory is fine, but I still get the wrong (null) date showing up in the events display.
Had to deactivate completely; pity as it looks like it has the potential to be really useful.