On a different web server, I had version 13.0.6474.20156. Creating this event wasn't an issue.
I then upgraded to version 13.0.6514.27391. Creating this event was still not an issue.
Finally, I navigated to "C:\Program Files (x86)\SmarterTools\SmarterTrack\MRS\Management\Settings\Modals". This directory was full of aspx files including the missing "fromEventAction.aspx" file.
I can try reinstalling again but if this doesn't extract the missing data, should I just manually replace the files in the Modals folder, from the working (good) webserver?