OJS Produce error on error log

My jurnal system has produce error code like below

[Fri Apr 21 09:52:45 2017] [error] [client] ojs2 has produced an error\n Message: USER ERROR: name lookup timed out\n In file: /var/www/html/lib/pkp/classes/webservice/WebService.inc.php\n At line: 226\n Stacktrace: \n Server info:\n OS: Linux\n PHP Version: 5.3.3\n Apache Version: Apache/2.2.15 (CentOS)\n DB Driver: mysql\n DB server version: 5.1.73, referer: https://jurnal.ugm.ac.id/jgki/issue/view/2273

Can anyone explain to me what I must to do to dissappear the error log above.

This seems to indicate that your server is trying to make a connection to another server, but can’t resolve the DNS name into an IP address for the connection.

You can get more information about what the context of this connect is by turning on show_stacktrace in config.inc.php.

thank you for answer…I’ll try to find out…