Hmm, that is odd.
I do see that your event pages at …events/upcoming/ and …events/month/ are available and functioning, so it seems just to affect the main events page at …/events/ – is that correct?
If so, in the first instance, can you try flushing the site’s rewrite rules? This is as simple as visiting the Permalink Settings page (you don’t need to change anything – just visiting it will cause WordPress to regenerate the list of rules).
If that doesn’t solve the problem can you run through the following steps from start to finish?
- Ensure The Events Calendar and Events Calendar PRO are up-to-date
- Deactivate all other plugins
- Switch to a default, unmodified theme such as Twenty Thirteen
- Repeat the permalink flush process
- Now test and see if the main events page is functioning as expected
If it does work after this, start reactivating everything one-at-a-time and see if the problem returns (taking note of whichever plugin/theme seems to trigger the problem if it returns).
Let me know how you get on!