when a host comes up,the thold stop working and

[pkwang]

Help!!!
When a host is down,the thold works fine,and can sent a alert e-mail,everying is ok.It has the following log in plugin clog.
05/11/2016 10:44:01 AM - SYSTEM STATS: Time:0.1597 Method:spine Processes:1 Threads:1 Hosts:2 HostsPerProcess:2 DataSources:0 RRDsProcessed:0
05/11/2016 10:43:01 AM - SYSTEM THOLD STATS: Time:0.0220 Tholds:0 DownHosts:0
But,when a host comes up,cacti didn't sent a alert e-mail,and since then,there is no thlod stats in clog,it looks like the thold doesn't work again.
05/11/2016 11:56:01 AM - SYSTEM STATS: Time:0.1605 Method:spine Processes:1 Threads:1 Hosts:2 HostsPerProcess:2 DataSources:0 RRDsProcessed:0
05/11/2016 11:55:02 AM - SYSTEM STATS: Time:0.1831 Method:spine Processes:1 Threads:1 Hosts:2 HostsPerProcess:2 DataSources:0 RRDsProcessed:0
I get the error when execute the code: "php /var/www/html/cacti/poller.php --force "
PHP Fatal error: Call to undefined function cacti_snmp_get() in /var/www/html/cacti/plugins/thold/includes/polling.php on line 188
This will continue until a host comes down again.
Please help me and forget my poor english,thanks!