Nagios installation issue

[Nivin Abraham]

my ubuntu version is 12.04
   nagios version is nagios-4.0.0beta4
   nagios plugin version is nagios-plugins-1.4.16

i have installed my host os is windows 7 
 vm used is oracle virtualbox

i followed the installation from youtube video Nagios sous Ubuntu 12.04 ~
Mohamed AKRICH

i followed the entire installation but changed the versions as mentioned
above everything got installed without any issues but when i type

"service nagios start"
and this is what i get 

/etc/init.d/nagios: 20 .:Can't open /etc/rc.d/init.d/functions




so pls help me and i am a newbie to linux as well as ubuntu


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