This only happens with wp_debug enabled.
Steps to reproduce:
I created a fresh install of WordPress with nothing but TEC, pro, community events, eventbrite, and filter bar. I go into the event settings and then the default content tab. I select a default country. I switch to the additional fields tab and then switch back to the default content tab.
I get this error for each country in the Default Country dropdown.
Notice: Array to string conversion in /Applications/MAMP/htdocs/tec/wp-includes/general-template.php on line 2408
I traced the error back to this file on line 535:
http://plugins.svn.wordpress.org/the-events-calendar/tags/3.5.1/lib/tribe-field.class.php
This might be a possible fix:
https://gist.github.com/embolden/c00f9497cb2574c2d0b5