helpful plugin

In some monitoring machines works fine.
But in a OMD-LAbs machine (nagios-engine) it doesn’t work.
Even if I install “perl -MCPAN -e ‘install Monitoring::Plugin'” or ‘Nagios::Plugin’ I receive this error:

root@monitoring:~# /omd/sites/mysite/lib/monitoring-plugins/check_qnapdisk -H my host address -w 4: -c 4: -T C -g 40 -l 45 -v -t 60
Can’t locate Nagios/Plugin.pm in @INC (you may need to install the Nagios::Plugin module) (@INC contains: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.26.1 /usr/local/share/perl/5.26.1 /usr/lib/x86_64-linux-gnu/perl5/5.26 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.26 /usr/share/perl/5.26 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at /omd/sites/mysite/lib/monitoring-plugins/check_qnapdisk line 24.
BEGIN failed–compilation aborted at /omd/sites/mysite/lib/monitoring-plugins/check_qnapdisk line 24.

Has anyone the same problem?

Thank you.
G.