Source code:
php/api/classes/class.cgraph.php:657
php/api/classes/class.cgraphprototype.php:652
self::exception(ZBX_API_ERROR_PARAMETERS, S_GRAPH.' [ '.$graph['name'].' ] '.S_GRAPH_TEMPLATE_HOST_CANNOT_OTHER_ITEMS_HOSTS_SMALL);

String:
'S_GRAPH_TEMPLATE_HOST_CANNOT_OTHER_ITEMS_HOSTS_SMALL'=>_('with template host cannot contain items from other hosts.'),

Documentation:
http://www.zabbix.com/documentation/1.8/manual/config/graphs

I propose to replace to something like: 'with items from template cannot contain items from other hosts.'
Please check logic and grammar too

And maybe you should even expand error message (or code too) according to documentation.