An estimated 20,000 Pokémon fans from all over the world converged on Grant Park last weekend for the first-ever Pokémon Go Fest, an event billed as a way for players to participate in special challenges, collect a variety of Pokémon, and meet other enthusiasts of the mobile game in person. Enthusiastic “trainers,” many in costume, stood in a line that wrapped around the park for hours on Saturday morning, excited about the possibility of battling and catching legendary Pokémon. To fend off dead batteries, many came wielding phone chargers. Some even brought multiple phones.

But when they got in the park, instead of legendary Pokémon, eager players were met by something even more menacing: technical difficulties. Overloaded servers and spotty cellular reception prevented some participants from logging into the game at all. Many who managed to access the game found that it crashed whenever they tried to catch a Pokémon. When Niantic CEO John Hanke was introduced as part of a presentation that was meant to kick off the event, he was met by boos and chants of “We can’t play!” and “Fix the game!”

Check out our video to see how the Fest unraveled.