Distributed Monitoring by node problem

[kadong]

where I installed zabbix server,and add the other node,all of them is ok.
but in the master node's dashboard, following this problem:
Warning: Invalid argument supplied for foreach() in /var/www/html/zabbix/include/blocks.inc.php on line 471

in the Last issues windows,

why?
who's can help me?
thanks.

[kadong]

it used mysql db;