Won’t open photos!! :(

Hi! I made photogallery:

https://www.zvono.gimnazijang.hr/2016/09/18/fotogalerija-s-maturalca-u-spanjolskoj-2016/

But when I open photo, I get this:
https://www.zvono.gimnazijang.hr/maturalac27/

(Catchable fatal error: Object of class WP_Error could not be converted to string in /home/gimnazij/zvono/wp-content/themes/enigma/functions.php on line 247)

Please, help. Thank you.