Keynote arrow keys aren't working

Hi, I have a MacBook Pro Retina Mid 2015 with El Capitan (v 10.11.4) and used Keynote (v 6.6.1) for a presentation. Everything was fine, but when i started the slideshow via the play button i couldn't advance through the slides with the arrow keys. The only key that worked in the slideshow was the 'esc' key. I deleted and reinstalled the app already, but nothing changed.