E_ERROR with EM v6

Hi

With Events Manager v6 this plug-in gives a critical error.

Een fout van het type E_ERROR werd veroorzaakt op regelnummer 73 van het bestand /var/web/vd19057/public_html/wp-content/plugins/stonehenge-em-cancellation/classes/class-admin.php. Foutmelding: Uncaught Error: Call to undefined function switch_to_blog() in /var/web/vd19057/public_html/wp-content/plugins/stonehenge-em-cancellation/classes/class-admin.php:73
Stack trace:
#0 /var/web/vd19057/public_html/wp-includes/class-wp-hook.php(307): Stonehenge_EM_Event_Cancellation_Admin->add_event_category('')
#1 /var/web/vd19057/public_html/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array)
#2 /var/web/vd19057/public_html/wp-includes/plugin.php(476): WP_Hook->do_action(Array)
#3 /var/web/vd19057/public_html/wp-settings.php(598): do_action('init')
#4 /var/web/vd19057/public_html/wp-config.php(83): require_once('/var/web/vd1905...')
#5 /var/web/vd19057/public_html/wp-load.php(50): require_once('/var/web/vd1905...')
#6 /var/web/vd19057/public_html/wp-admin/admin.php(34): require_once('/var/web/vd1905...')
#7 /var/web/vd19057/public_html/wp-admin/update.php(16): require_once('/var/web/vd1905...')
#8 {main}
  thrown