S2·E18 Vertigo

After a trip to the Carthage Region, Jeremie believes he has the data necessary to cure Aelita's virus. While the two work on the cure, Odd, Ulrich, and Yumi go to a rock climbing contest. Odd races against Hervé, who is no match for Odd. William then goads Ulrich into racing, despite his obvious reluctance. During the race, Ulrich gets dizzy and falls. Yumi realizes that he must have vertigo. Ulrich, embarrassed, runs off. Meanwhile, Jeremie finds the anti-virus and gives it to Aelita. Despite some problem with the application, it seems to work. However, this does not last. An error in the anti-virus causes her to turn invisible. On top of that, she can't enter the towers on Lyoko, making it impossible for her to stop Xana's latest attack, which is a possessed pack of wolves targeting Odd, Ulrich, and Yumi.