Howdy,
Some users were able to resolve this problem over in this thread: https://www.ads-software.com/support/topic/single-events-page-not-found
This issue crops up from time to time, but often each person’s fix is unique. If none of the solutions in that thread work for you, could you mind try enabling the default 2013 theme? Did that fix it? If not, what about disabling all plugins except Tribe ones. Is it working now?
If either of those fixes it for you, then you are facing a conflict between your plugins or your theme and The Events Calendar. In which case we could advise you on how best to integrate the two over at https://tri.be/support/forums/, but you will need to purchase a PRO license. That license comes with a year of 5+ day/week PRO support (the free version comes with courtesy support, which is very limited), and many other benefits.
Even still sometimes integrations can get super tricky if one of your other plugins or your theme has deviated from WordPress’ best practice. In which case, you might want more than our advice and assistance, you might want to hire a developer to just integrate things for you. Or, perhaps you should look for an alternative theme or plugin.
I hope that helps. Cheers!
– Brook