Hi Emmanuelle – there is unfortunately a known bug here that we hope to address shortly. Right now though if you familiarize yourself with the Themer’s Guide you can workaround this as follows:
1. Set up a custom single-event.php template (ie, in your-theme/tribe-events/single-event.php) and base this on the original in the-events-calendar/views/single-event.php.
2. Locate the following line of code:
<?php if( get_post_type() == TribeEvents::POSTTYPE && tribe_get_option( 'showComments','no' ) == 'yes' ) { comments_template(); } ?>
3. Try changing this to:
<?php if( get_post_type() == TribeEvents::POSTTYPE && tribe_get_option( 'showComments', false ) ) { comments_template(); } ?>
Does that help at all?