[syslog-ng]Question about program()

[Hyunmoo Rhee]

I installed syslog-ng-1.4.8 yesterday. but program() wasn't operate. why it doesn't operate?
my syslog-ng.conf is here.
=====================================START========================
options { use_dns(no); };

source router_src { 
        udp(port(514));
};

destination router_total_log {
        file("/root/logfile/router_total_log");
        program(/root/sample.sh);
};

destination deny_tcp_all_log {
        file("/root/logfile/deny_tcp_all_log");
};

destination deny_udp_all_log {
        file("/root/logfile/deny_udp_all_log");
};

filter deny_tcp_all {
        match("tcp");
};

filter deny_udp_all {
        match("udp");
};

log {
        source(router_src);
        destination(router_total_log);
};

log {
        source(router_src);
        filter(deny_tcp_all);
        destination(deny_tcp_all_log);
};

log {
        source(router_src);
        filter(deny_udp_all);
};
=================================END======================

sample.sh is simple script. (echo asdf >> /root/sample.txt)
but doesn't operate. shell script permission is 755.
.....