This function will disable the NextGen gallery plugin's output buffering that breaks the Espresso API JSON feed. Add this to your theme's functions.php file or your own custom functionality plugin.

ngg_play_fair.php

<?php

// Please do NOT include the opening php tag 

/* Wrangle NextGen Gallery so it doesn't break the json API */

add_action( 'init','ee_nextgen_play_fair',1 );

function ee_nextgen_play_fair(){
  if( preg_match( "/espresso-api/", $_SERVER['REQUEST_URI'] ) ){
    add_filter( 'run_ngg_resource_manager','__return_false' );
  }
}