API-login error

Hi, im new to opencart and when i try to change order status this happen and dont change order status



and the register log show this after i try to change any order status

2015-06-12 7:32:12 - PHP Warning: json_encode(): Invalid UTF-8 sequence in argument in /var/www/vhosts/96/243934/webspace/httpdocs/electrotecnia.com/loja/catalog/controller/api/login.php on line 37

line 37 is :


any solutions?