We tested it on 2.6 beta 1 and as I see you put code in appropriate place. One more thing - are you using also vBSEO? We tested it with vBSEO only.
Please check also this solution. Replace:
by:PHP Code:
require_once(DIR. '/includes/vbenterprisetranslator_functions_vbseo.php');
Also if you have any more specific error log/message it would be helpfulPHP Code:
require_once(dirname(__FILE__) . '/../includes/vbenterprisetranslator_functions_vbseo.php');