Hi agueso,
thanks for your fast reply. I disabled the theme and everything worked like a charme. I found that I had overwritten the file in the [your-theme]/tribe-events/day/content.php folder. I got rid of the header nav.
By accident I also removed the action <?php do_action( ‘tribe_events_before_header’ ); ?>.
I put this action back in the template. It works now.
Thank you!
Regards.