Error Message during Domainmapping

Hi,
i got this errormessage activating the Domainmapping:
Warning: dns_get_record() [function.dns-get-record]: res_nsend() failed in /var/www/web709/html/wp-content/plugins/domain-mapping/classes/Domainmap/Render/Network/Options.php on line 122

Warning: Invalid argument supplied for foreach() in /var/www/web709/html/wp-includes/functions.php on line 2713

What can i do?

thanks for help