This is the first clue:
ldomain (Cron Daemon)
Subject: Cron <root@localhost> /home/mrourmon/bin/omupdate.sh
Your cron job /home/mrourmon/bin/omupdate.sh is failing. Its failing because
cp: cannot stat `/home/mrourmon/tmp/mon.lite': No such file or directory
Can't locate RRDs.pm in @INC (@INC contains: /usr/local/rrdtool-1.0.49/lib/perl ../lib/perl etc
at /home/mrourmon/bin/omupdate.pl line 42.
BEGIN failed--compilation aborted at /home/mrourmon/bin/omupdate.pl line 42.
Basically you need to read the shell source and make sure the files it expects are where they should be.
You need to use the CPAN tool to install RRDs.pm (at least). The Perl prog needs this and other files.
To install from CPAN, login as root and
perl -e shell -M CPAN
cpan> install RRDs
To check a perl prog for syntax without running it, try
perl -wc file.pl
There should be some docs for this stuff that specify what you need to setup to make it run.