Just in case my experience may help diagnosing this type of problem:
When I first installed the plugin, the calendar view would show up OK, but clicking the event list button or even the calendar button would result in a 404 error. My site is in French: the URLs being generated were […]/a-venir/ and […]/mois/. Both valid URLs: it looks like the first one was generated from the string “à venir” in the French translation, and the accent was stripped. Still, neither URL worked.
I discovered I could see either view by accessing […]/upcoming/ and […]/month/ instead. So, the plugin generated each view at the default English URL but referred to the French language file when creating links to those pages.
My WordPress installation is a bit atypical: I’m running multiple sites in two languages (French and English) and using the Backend Localization plugin to keep the back end in English no matter which site I’m working on. Still, the French URLs don’t work even if I switch the back end to French…
I wound up editing the French translation in Poedit so the plugin would translate “upcoming” to “upcoming” and “month” to “month”. Seems to work fine now; I’m just not sure why it wouldn’t work before.