Install nagios3 on debian by apt, file not found error

Install nagios3 on debian by apt, file not found error

I have a Wheezy debian, and I've installed nagios3 using apt-get. When I
go to myhost.com/nagios3 and then go to a page, for example Tactical
Overview I get the error message
The requested URL /cgi-bin/nagios3/tac.cgi was not found on this server.
which is odd.
These lines are in /etc/apache2/conf.d/nagios3.conf:
ScriptAlias /cgi-bin/nagios3 /usr/lib/cgi-bin/nagios3
ScriptAlias /nagios3/cgi-bin /usr/lib/cgi-bin/nagios3
And this is output of ls /usr/lib/cgi-bin/nagios3:
avail.cgi config.cgi graphs.cgi history.cgi outages.cgi
rrd2-system.cgi status.cgi statuswml.cgi summary.cgi trends.cgi
cmd.cgi extinfo.cgi histogram.cgi notifications.cgi rrd2-graph.cgi
showlog.cgi statusmap.cgi statuswrl.cgi tac.cgi
What's going on here?